全文获取类型
收费全文 | 4044篇 |
免费 | 262篇 |
国内免费 | 2篇 |
出版年
2023年 | 17篇 |
2022年 | 41篇 |
2021年 | 99篇 |
2020年 | 59篇 |
2019年 | 71篇 |
2018年 | 101篇 |
2017年 | 93篇 |
2016年 | 133篇 |
2015年 | 217篇 |
2014年 | 197篇 |
2013年 | 283篇 |
2012年 | 340篇 |
2011年 | 362篇 |
2010年 | 218篇 |
2009年 | 180篇 |
2008年 | 249篇 |
2007年 | 243篇 |
2006年 | 207篇 |
2005年 | 205篇 |
2004年 | 173篇 |
2003年 | 170篇 |
2002年 | 146篇 |
2001年 | 38篇 |
2000年 | 32篇 |
1999年 | 24篇 |
1998年 | 34篇 |
1997年 | 31篇 |
1996年 | 23篇 |
1995年 | 25篇 |
1994年 | 19篇 |
1993年 | 30篇 |
1992年 | 16篇 |
1991年 | 9篇 |
1990年 | 16篇 |
1989年 | 14篇 |
1988年 | 8篇 |
1987年 | 11篇 |
1986年 | 11篇 |
1985年 | 12篇 |
1984年 | 16篇 |
1983年 | 11篇 |
1982年 | 17篇 |
1981年 | 6篇 |
1980年 | 12篇 |
1979年 | 9篇 |
1977年 | 7篇 |
1976年 | 6篇 |
1975年 | 6篇 |
1974年 | 16篇 |
1966年 | 5篇 |
排序方式: 共有4308条查询结果,搜索用时 890 毫秒
941.
Andrade Elisa Helena Paz Figueiredo Leandra Barcelos Vilela Ana Paula Pessoa Rosa Jlio Csar Cmara Zibaoui Hassan Melo Kroon Erna Geessien 《EcoHealth》2022,19(1):75-84
EcoHealth - Dengue virus (DENV) 1–4 is the etiological agent of dengue, the most important viral infection transmitted by Aedes spp mosquitoes to humans. Our goal was to identify the... 相似文献
942.
Tamíris A. Araújo Lúcia Helena A. Araújo Nilson R. Silva Carlos Eduardo A. Luz zio M. da Silva Mrcio D. Moreira Fbio A. Suinaga Marcelo C. Picano Cristina S. Bastos 《Journal of Applied Entomology》2019,143(8):893-901
A standardized sampling plan is the starting point for developing a decision‐making system for pest control. Aphis gossypii (Hemiptera: Aphididae) is a destructive sap‐feeding pest on cotton worldwide. However, research addressing cotton cultivar, plant phenology and field size with the aim of developing a sampling plan for A. gossypii has not been done. Therefore, in this study, we developed a standardized sampling for A. gossypii as a function of these factors. To accomplish this, A. gossypii densities in four experimental cotton cultivars were sampled weekly during year one to determine the ideal aphid characteristic to sample (by individual or colony). During year one and two, A. gossypii densities were sampled weekly in the same cultivars to determine sampling unit, sampling technique and the number of samples for an A. gossypii sampling plan. Using the sample number determined, the sampling time was recorded for cotton field size of 1, 5, 10, 50, 100 and 150 ha in order to estimate the sampling cost. In cotton, the count of individuals was the best characteristic for the assessment of A. gossypii. Leaves of the most apical branches for the vegetative and reproductive cotton plant stage were the best sampling units. The best sampling technique was direct counting. The cotton cultivar did not affect the development of the sampling plan. The A. gossypii sampling plan involved the evaluation of 58 samples per zone and required 20 min (<0.35 min/sample) for the evaluation of these samples. However, the walking time between samples was the main factor responsible for the total sampling time and cost in cotton fields, and this factor strongly depends on the size of the cotton field. 相似文献
943.
Usva Kirsi Virtanen Eetu Hyvärinen Helena Nousiainen Jouni Sinkko Taija Kurppa Sirpa 《The International Journal of Life Cycle Assessment》2019,24(2):351-361
The International Journal of Life Cycle Assessment - Food production without consuming scarce local freshwater resources in an unsustainable way needs to be ensured. A robust method to assess water... 相似文献
944.
The range of pathologies that lymph node (LN) fine needle cytology (FNC) may encounter is extremely wide and ancillary techniques, in addition to traditional smears, are generally required to reach reliable cytologic diagnoses. Storing part of the cytologic material may be useful or necessary for molecular testing. The main difficulties concern the generally small size of the sample and the different methods of acquisition of LN‐FNC. Therefore, the preanalytic phase is extremely important for LN‐FNC. This article outlines the management of LN‐FNC material, vials, technical devices (e.g.: additional smears, cytospin slides, LBC slides, cards, resins, etc.) and main ancillary techniques to assess their optimal application, taking into account the different diagnostic needs and cell storage. 相似文献
945.
946.
Yun Xu Sarah J. Dixon Richard G. Brereton Helena A. Soini Milos V. Novotny Karlheinz Trebesius Ingrid Bergmaier Elisabeth Oberzaucher Karl Grammer Dustin J. Penn 《Metabolomics : Official journal of the Metabolomic Society》2007,3(4):427-437
Several studies have shown that microbial action is responsible for many compounds responsible for human odour. In this paper,
we compare the pattern of microbial profiles and that of chemical profiles of human axillary odour by using multivariate pattern
matching techniques. Approximately 200 subjects from Carinthia, Austria, participated in the study. The microbial profiles
were represented by denaturing gradient gel electrophoresis (DGGE) analysis and the axillary odour profiles were determined
in the sweat samples collected by a stir-bar sampling device and analysed by gas chromatography/mass spectrometry (GC/MS).
Both qualitative and quantitative distance metrics were used to construct dissimilarity matrices between samples which were
then used to represent the patterns of these two types of profiles. The distance matrices were then compared by using the
Mantel test and the Procrustean test. The results show that on the overall dataset there is no strong correlation between
microbial and chemical profiles. When the data are split into family groups, correlations vary according to family with a
range of estimated p values from 0.00 to 0.90 that the null hypothesis (no correlation) holds. When 32 subjects who followed four basic rules
of behaviour were selected, the estimated p-values are 0.00 using qualitative and <0.01 using quantitative distance metrics, suggesting excellent evidence that there
is a connection between the microbial and chemical signature. 相似文献
947.
Bernardo R Tura Helena F Martino Luis H Gowdak Ricardo Ribeiro dos Santos Hans F Dohmann José E Krieger Gilson Feitosa Fábio Vilas-Boas Sérgio A Oliveira Suzana A Silva Augusto Z Bozza Radovan Borojevic Antonio C Campos de Carvalho 《Trials》2007,8(1):1-4
Background
Cardiovascular diseases are the major cause of death in the world. Current treatments have not been able to reverse this scenario, creating the need for the development of new therapies. Cell therapies have emerged as an alternative for cardiac diseases of distinct causes in experimental animal studies and more recently in clinical trials.Method/Design
We have designed clinical trials to test for the efficacy of autologous bone marrow derived mononuclear cell therapies in four different cardiopathies: acute and chronic ischemic heart disease, and Chagasic and dilated cardiomyopathy. All trials are multicenter, randomized, double-blind and placebo controlled. In each trial 300 patients will be enrolled and receive optimized therapy for their specific condition. Additionally, half of the patients will receive the autologous bone marrow cells while the other half will receive placebo (saline with 5% autologous serum). For each trial there are specific inclusion and exclusion criteria and the method for cell delivery is intramyocardial for the chronic ischemic heart disease and intracoronary for all others. Primary endpoint for all studies will be the difference in ejection fraction (determined by Simpson's rule) six and twelve months after intervention in relation to the basal ejection fraction. The main hypothesis of this study is that the patients who receive the autologous bone-marrow stem cell implant will have after a 6 month follow-up a mean increase of 5% in absolute left ventricular ejection fraction in comparison with the control group.Discussion
Many phase I clinical trials using cell therapy for cardiac diseases have already been performed. The few randomized studies have yielded conflicting results, rendering necessary larger well controlled trials to test for efficacy of cell therapies in cardiopathies. The trials registration numbers at the NIH registry are the following: Chagasic cardiomyopathy (NCT00349271), dilated cardiomyopathy (NCT00333827), acute myocardial infarction (NCT00350766) and Chronic Ischemic Heart Disease (NCT00362388). 相似文献948.
Ferron SR Andreu-Agullo C Mira H Sanchez P Marques-Torrejon MA Farinas I 《Nature protocols》2007,2(4):849-859
We describe a protocol developed/modified by our group for the ex vivo and in vivo assessment of the response to a soluble factor of murine neural stem cells from the adult sub-ventricular zone (SVZ). The procedure includes several experimental options that can be used either independently or in combination. Potential factor effects on self-renewal, survival and proliferation are assayed by means of neurosphere cultures, with the factor administered directly in vitro to the culture plates (Step 1) or infused in vivo immediately before tissue dissociation (Step 3). We also use bromodeoxiuridine (BrdU) retention to label slowly dividing cells in vivo and subsequently perform two different types of experiments. In one set of experiments, the factor is added to primary cultures of stem cells obtained from the BrdU-pulsed animals and effects are tested on label-retaining cells after immunocytochemistry (Step 2). In another set, prolonged intraventricular infusion of the factor in BrdU-pulsed animals is followed by immunohistochemical analysis of BrdU labeling in the intact SVZ (Step 4). The minimum estimated time for the full combined procedure is 45 d. 相似文献
949.
The growing number of applications to determine the stoichiometry, interactions and even subunit architecture of protein complexes from mass spectra suggests that some general guidelines can now be proposed. In this protocol, we describe the necessary steps required to maintain interactions between subunits in the gas phase. We begin with the preparation of suitable solutions for electrospray (ES) and then consider the transmission of complexes through the various stages of the mass spectrometer until their detection. Subsequent steps are also described, including the dissociation of these complexes into multiple subcomplexes for generation of interaction networks. Throughout we highlight the critical experimental factors that determine success. Overall, we develop a generic protocol that can be carried out using commercially available ES mass spectrometers without extensive modification. 相似文献
950.
Differential scanning fluorimetry (DSF) is a rapid and inexpensive screening method to identify low-molecular-weight ligands that bind and stabilize purified proteins. The temperature at which a protein unfolds is measured by an increase in the fluorescence of a dye with affinity for hydrophobic parts of the protein, which are exposed as the protein unfolds. A simple fitting procedure allows quick calculation of the transition midpoint; the difference in the temperature of this midpoint in the presence and absence of ligand is related to the binding affinity of the small molecule, which can be a low-molecular-weight compound, a peptide or a nucleic acid. DSF is best performed using a conventional real-time PCR instrument. Ligand solutions from a storage plate are added to a solution of protein and dye, distributed into the wells of the PCR plate and fluorescence intensity measured as the temperature is raised gradually. Results can be obtained in a single day. 相似文献