全文获取类型
收费全文 | 8534篇 |
免费 | 557篇 |
国内免费 | 1篇 |
专业分类
9092篇 |
出版年
2023年 | 43篇 |
2022年 | 93篇 |
2021年 | 172篇 |
2020年 | 95篇 |
2019年 | 157篇 |
2018年 | 213篇 |
2017年 | 157篇 |
2016年 | 272篇 |
2015年 | 406篇 |
2014年 | 471篇 |
2013年 | 576篇 |
2012年 | 733篇 |
2011年 | 651篇 |
2010年 | 427篇 |
2009年 | 423篇 |
2008年 | 558篇 |
2007年 | 517篇 |
2006年 | 451篇 |
2005年 | 471篇 |
2004年 | 415篇 |
2003年 | 386篇 |
2002年 | 367篇 |
2001年 | 75篇 |
2000年 | 58篇 |
1999年 | 76篇 |
1998年 | 93篇 |
1997年 | 68篇 |
1996年 | 67篇 |
1995年 | 46篇 |
1994年 | 66篇 |
1993年 | 46篇 |
1992年 | 44篇 |
1991年 | 40篇 |
1990年 | 30篇 |
1989年 | 30篇 |
1988年 | 23篇 |
1987年 | 15篇 |
1986年 | 11篇 |
1985年 | 15篇 |
1984年 | 21篇 |
1983年 | 13篇 |
1982年 | 22篇 |
1981年 | 16篇 |
1980年 | 13篇 |
1979年 | 9篇 |
1978年 | 17篇 |
1977年 | 13篇 |
1976年 | 14篇 |
1975年 | 10篇 |
1938年 | 8篇 |
排序方式: 共有9092条查询结果,搜索用时 15 毫秒
71.
Bartolomeo Lercari Franco Tognoni Roberto Lorenzi Alberto Manetti 《Plant biosystems》2013,147(3):147-156
Abstract Growth response of coleoptile sections from four Italian cultivars of wheat to some growth regulators.—The following Italian wheat varieties were used to obtain the coleoptile sections used throughout the experiments: Funo, S. Pastore, Abbondanza, Generoso. The growth substances tested were Indolacetic acid (IAA), Abscisic acid (ABA), Kinetin and Gibberellic acid. The colcoptile response of each variety was tested with three different concentrations for each growth regulator in combination with two sucrose concentrations and three different pH levels. The experiments indicated that the coleoptiles from the variety « Funo » react linearly to incresing IAA and ABA concentration resulting the best one to be used in this bioassay. 相似文献
72.
73.
Nicola Bizzaro Elena Bartoloni Gabriella Morozzi Stefania Manganelli Valeria Riccieri Paola Sabatini Matteo Filippini Marilina Tampoia Antonella Afeltra Giandomenico Sebastiani Claudia Alpini Vittorio Bini Onelia Bistoni Alessia Alunno Roberto Gerli 《Arthritis research & therapy》2013,15(1):R16
Introduction
The diagnostic, predictive and prognostic role of anti-cyclic citrullinated peptide (CCP) antibodies in rheumatoid arthritis (RA) patients is widely accepted. Moreover, detection of these antibodies in subjects presenting with undifferentiated arthritis (UA) is associated with a significant risk to develop the disease. On the other hand, clinical and prognostic significance of evaluating anti-CCP levels in subjects with inflammatory arthritis at disease onset has not been fully clarified. The goal of this prospective study is to analyze the value and prognostic significance of anti-CCP titer quantification in UA subjects.Methods
Serial anti-CCP assays were measured in 192 consecutive patients presenting with UA lasting less than 12 weeks. Clinical and serological data and arthritis outcome were evaluated every 6 months until two years of follow-up.Results
Anti-CCP positivity, at both low and high titer, and arthritis of hand joints significantly predicted RA at two years, risk increasing in subjects with high anti-CCP titers at baseline. Moreover, time to RA diagnosis was shorter in patients with high anti-CCP2 titers at enrollment with respect to those with low antibody concentration.Conclusions
Presence of anti-CCP antibodies, at both low and high concentration, is significantly associated with RA development in subjects with recent onset UA. However, time interval from the onset of the first symptoms to the fulfilment of the classification criteria appears to be directly related to the initial anti-CCP level. 相似文献74.
Luca Carmignani Roberto Bianchi Gabriele Cozzi Angelica Grasso Nicola Macchione Carlo Marenghi Sara Melegari Marco Rosso Elena Tondelli Augusto Maggioni 《Reviews in urology》2013,15(4):145-153
A review of the literature was performed to summarize current evidence regarding the efficacy of topical immunotherapy and chemotherapy for upper urinary tract urothelial cell carcinoma (UUT-UCC) in terms of post-treatment recurrence rates. A Medline database literature search was performed in March 2012 using the terms upper urinary tract, urothelial cancer, bacillus Calmette-Guérin (BCG), and mitomycin C. A total of 22 full-text articles were assessed for eligibility, and 19 studies reporting the outcomes of patients who underwent immunotherapy or chemotherapy with curative or adjuvant intent for UUT-UCC were chosen for quantitative analysis. Overall, the role of immunotherapy and chemotherapy for UUT-UCC is not firmly established. The most established practice is the treatment of carcinoma in situ (CIS) with BCG, even if a significant advantage has not yet been proven. The use of BCG as adjuvant therapy after complete resection of papillary UUT-UCC has been studied less extensively, even if recurrence rates are not significantly different than after the treatment of CIS. Only a few reports describe the use of mitomycin C, making it difficult to obtain significant evidence.Key words: Upper urinary tract, Urothelial cell carcinoma, Bacillus Calmette-Guérin, Mitomycin C, Chemotherapy, ImmunotherapyAccording to the 2011 update of the European Guidelines for the diagnosis and management of upper urinary tract urothelial cell carcinoma (UUT-UCC),1 urothelial carcinomas are the fourth most common tumors after prostate and breast cancer, lung cancer, and colorectal cancer. Bladder tumors account for 90% to 95% of urothelial carcinomas; UUT-UCC are relatively uncommon and account for only 5% to 10% of urothelial carcinomas. The annual incidence of UUT-UCC in Western countries is approximately one or two new cases per 100,000 inhabitants. Pyelocaliceal tumors are approximately twice as common as ureteral tumors. In 8% to 13% of cases, concurrent bladder cancer is present, and 60% of UUT-UCC are invasive at diagnosis, compared with only 15% of bladder tumors. This kind of carcinoma has a peak incidence in people in their 70s and 80s, with a higher prevalence in men.Radical nephroureterectomy (RNU) with excision of the bladder cuff represents the gold standard treatment for UUT-UCC, regardless of the location of the tumor in the upper urinary tract.1 Lymph node dissection associated with RNU is of therapeutic interest and allows for optimal staging of the disease.Conservative surgery for low-risk UUT-UCC allows for preservation of the upper urinary renal unit; conservative management can be considered in imperative cases (renal insufficiency, solitary functional kidney) or in elective cases (ie, when the contralateral kidney is functional) for low-grade, low-stage tumors. Endoscopic ablation can be considered if a flexible ureteroscope, laser generator, and pliers (pluck) for biopsies are available, if the patient is informed of the need for closer follow-up, and if a complete resection is advocated.Segmental ureteral resection with wide margins provides adequate pathologic specimens for definitive staging and grade analysis while also preserving the ipsilateral kidney. Segmental resection is possible for the treatment of low- and high-risk tumors of the distal ureter, whereas segmental resection of the iliac and lumbar ureter is associated with a greater failure rate. Open resection of tumors of the renal pelvis or calices has almost disappeared.Percutaneous management can be considered for low-grade or noninvasive UUT-UCC that are inaccessible or difficult to manage by ureteroscopy, even if a theoretical risk of seeding exits in the puncture tract and if perforations occur during the procedure.After conservative treatment of UUT-UCC or for the treatment of carcinoma in situ (CIS), the instillation of bacillus Calmette-Guérin (BCG) or mitomycin C (MMC) is technically feasible by means of a percutaneous nephrostomy or even through a ureteric stent.Different agents have been used for topical therapy, including BCG, MMC, epirubicine, and thiotepa. Topical chemotherapeutic agents can be administered after endoscopic management, whereas instillations of BCG need to be postponed until the urothelium heals to avoid systemic side effects.According to a recent review,2 topical therapy appears to be safe, although its efficacy is debatable. Complications from the administration of topical immunotherapy or chemotherapy can be avoided by maintaining low intracavitary pressures during administration. Renal function does not seem to be impaired after instillation of BCG or MMC.3 No systemic side effects result from perfusion with MMC, and persistent fever was reported in 5% of patients in combined major series after BCG administration; therefore, this side effect was resolved with appropriate antimicrobial therapy in all cases. Furthermore, up to 25% of patients may have granulomatous involvement of the urinary tract after BCG.This review summarizes current evidence about the efficacy of topical immunotherapy and chemotherapy in terms of post-treatment recurrence rates. 相似文献
75.
Soil Loss and Runoff in Semiarid Ecosystems: A Complex Interaction Between Biological Soil Crusts, Micro-topography, and Hydrological Drivers 总被引:1,自引:0,他引:1
Emilio Rodríguez-Caballero Yolanda Cantón Sonia Chamizo Roberto Lázaro Adrián Escudero 《Ecosystems》2013,16(4):529-546
Biological soil crusts (BSCs) cover non-vegetated areas in most arid and semiarid ecosystems. BSCs play a crucial role in the redistribution of water and sediments and, ultimately, in the maintenance of ecosystem function. The effects of BSCs on water infiltration are complex. BSCs increase porosity and micro-topography, thus enhancing infiltration, but, at the same time, they can increase runoff by the secretion of hydrophobic compounds and clogging of soil pores upon wetting. BSCs confer stability on soil surfaces, reducing soil detachment locally; however, they can also increase runoff, which may increase sediment yield. Although the key role of BSCs in controlling infiltration–runoff and erosion is commonly accepted, conflicting evidence has been reported concerning the influence of BSCs on runoff generation. Very little is known about the relative importance of different BSC features such as cover, composition, roughness, or water repellency, and the interactions of these attributes in runoff and erosion. Because BSC characteristics can affect water flows and erosion both directly and indirectly, we examined the direct and indirect effects of different BSC features on runoff and erosion in a semiarid ecosystem under conditions of natural rainfall. We built structural equation models to determine the relative importance of BSC cover and type and their derived surface attributes controlling runoff and soil erosion. Our results show that the hydrological response of BSCs varies depending on rainfall properties, which, in turn, determine the process governing overland flow generation. During intense rainfalls, runoff is controlled not only by rainfall intensity but also by BSC cover, which exerts a strong direct and indirect influence on infiltration and surface hydrophobicity. Surface hydrophobicity was especially high for lichen BSCs, thus masking the positive effect of lichen crust on infiltration, and explaining the lower infiltration rates recorded on lichen than on cyanobacterial BSCs. Under low intensity, rainfall volume exerts a stronger effect than rainfall intensity, and BSC features play a secondary role in runoff generation, reducing runoff through their effect on surface micro-topography. Under these conditions, lichen BSCs presented higher infiltration rates than cyanobacterial BSCs. Our results highlight the significant protective effect against erosion exerted by BSCs at the plot scale, enhancing surface stability and reducing sediment yield in both high- and low-magnitude rainfall events. 相似文献
76.
Simone Accordini Angelo Guido Corsico Isa Cerveri Leonardo Antonicelli Francesco Attena Roberto Bono Lucio Casali Marcello Ferrari Alessandro Fois Pierpaolo Marchetti Pietro Pirina Roberta Tassinari Giuseppe Verlato Roberto de Marco 《Respiratory research》2013,14(1):16
Background
No study has been carried out on the time trend in the prevalence of chronic bronchitis (CB) in recent years, despite its clinical and epidemiological relevance. We evaluated the trend in CB prevalence during the past decade among young Italian adults.Methods
A screening questionnaire was mailed to general population samples of 20–44 year-old subjects in two cross-sectional surveys: the Italian Study on Asthma in Young Adults (ISAYA) (1998/2000; n = 18,873, 9 centres) and the screening stage of the Gene Environment Interactions in Respiratory Diseases (GEIRD) study (2007/2010; n = 10,494, 7 centres). CB was defined as having cough and phlegm on most days for a minimum of 3 months a year and for at least 2 successive years. The prevalence rates and the risk ratios (RRs) for the association between CB and each potential predictor were adjusted for gender, age, season of response, type of contact, cumulative response rate, and centre.Results
CB prevalence was 12.5% (95% CI: 12.1-12.9%) in 1998/2000 and 12.6% (95% CI: 11.7-13.7%) in 2007/2010; it increased among never smokers (from 7.6 to 9.1%, p = 0.003), current light smokers (<15 pack-years; from 15.1 to 18.6%, p < 0.001), and unemployed/retired subjects (from 14.3 to 19.1%, p = 0.001). In this decade, the prevalence of current smoking decreased (from 33.6 to 26.9%, p < 0.001), whereas the prevalence of unemployment/premature retirement (from 5.3 to 6.0%, p = 0.005), asthma (from 5.0 to 6.2%, p = 0.003), and allergic rhinitis (from 19.5 to 24.5%, p < 0.001) increased. In both 1998/2000 and 2007/2010, the likelihood of having CB was significantly higher for women, current smokers, asthmatic patients, and subjects with allergic rhinitis. During this period, the strength of the association between CB and current heavy smoking (≥15 pack-years) decreased (RR: from 4.82 to 3.57, p = 0.018), whereas it increased for unemployment/premature retirement (from 1.11 to 1.53, p = 0.019); no change was observed for gender, asthma, and allergic rhinitis.Conclusions
Despite the significant reduction in current smoking, CB prevalence did not vary among young Italian adults. The temporal pattern of CB prevalence can only be partly explained by the increase of unemployment/premature retirement, asthma and allergic rhinitis, and suggests that other factors could have played a role. 相似文献77.
78.
Teresa M. Zotes Roberto Spada Vladimir Mulens Sonia Pérez-Yagüe Carlos O. Sorzano Klaus Okkenhaug Ana C. Carrera Domingo F. Barber 《PloS one》2013,8(8)
The role of p110δ PI3K in lymphoid cells has been studied extensively, showing its importance in immune cell differentiation, activation and development. Altered T cell localization in p110δ-deficient mouse spleen suggested a role for p110δ in non-hematopoietic stromal cells, which maintain hematopoietic cell segregation. We tested this hypothesis using p110δWT/WT mouse bone marrow to reconstitute lethally irradiated p110δWT/WT or p110δD910A/D910A (which express catalytically inactive p110δ) recipients, and studied localization, number and percentage of hematopoietic cell subsets in spleen and lymph nodes, in homeostatic conditions and after antigen stimulation. These analyses showed diffuse T cell areas in p110δD910A/D910A and in reconstituted p110δD910A/D910A mice in homeostatic conditions. In these mice, spleen CD4+ and CD8+ T cell numbers did not increase in response to antigen, suggesting that a p110δD910A/D910A stroma defect impedes correct T cell response. FACS analysis of spleen stromal cell populations showed a decrease in the percentage of gp38−CD31+ cells in p110δD910A/D910A mice. qRT-PCR studies detected p110δ mRNA expression in p110δWT/WT spleen gp38−CD31+ and gp38+CD31+ subsets, which was reduced in p110δD910A/D910A spleen. Lack of p110δ activity in these cell populations correlated with lower LTβR, CCL19 and CCL21 mRNA levels; these molecules participate in T cell localization to specific spleen areas. Our results could explain the lower T cell numbers and more diffuse T cell areas found in p110δD910A/D910A mouse spleen, as well as the lower T cell expansion after antigen stimulation in p110δD910A/D910A compared with p110δWT/WT mice. 相似文献
79.
80.
Rafaela T. P. Sant'Anna Emily V. Monteiro Juliano R. T. Pereira Roberto B. Faria 《PloS one》2013,8(12)
This work presents a new clock reaction based on ozone, iodine, and chlorate that differs from the known chlorate-iodine clock reaction because it does not require UV light. The induction period for this new clock reaction depends inversely on the initial concentrations of ozone, chlorate, and perchloric acid but is independent of the initial iodine concentration. The proposed mechanism considers the reaction of ozone and iodide to form HOI, which is a key species for producing non-linear autocatalytic behavior. The novelty of this system lies in the presence of ozone, whose participation has never been observed in complex systems such as clock or oscillating reactions. Thus, the autocatalysis demonstrated in this new clock reaction should open the possibility for a new family of oscillating reactions. 相似文献