首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   7763篇
  免费   671篇
  国内免费   6篇
  2023年   19篇
  2022年   25篇
  2021年   92篇
  2020年   63篇
  2019年   110篇
  2018年   153篇
  2017年   115篇
  2016年   238篇
  2015年   364篇
  2014年   426篇
  2013年   437篇
  2012年   553篇
  2011年   563篇
  2010年   352篇
  2009年   329篇
  2008年   455篇
  2007年   435篇
  2006年   394篇
  2005年   397篇
  2004年   399篇
  2003年   351篇
  2002年   314篇
  2001年   303篇
  2000年   242篇
  1999年   214篇
  1998年   73篇
  1997年   76篇
  1996年   54篇
  1995年   58篇
  1994年   37篇
  1993年   27篇
  1992年   77篇
  1991年   83篇
  1990年   50篇
  1989年   54篇
  1988年   46篇
  1987年   45篇
  1986年   32篇
  1985年   35篇
  1984年   33篇
  1982年   20篇
  1981年   18篇
  1979年   19篇
  1978年   22篇
  1977年   24篇
  1976年   24篇
  1974年   24篇
  1973年   19篇
  1971年   20篇
  1970年   17篇
排序方式: 共有8440条查询结果,搜索用时 16 毫秒
31.
Range of motion (ROM) measurements are essential for the evaluation for and diagnosis of adhesive capsulitis of the shoulder (AC). However, taking these measurements using a goniometer is inconvenient and sometimes unreliable. The Kinect (Microsoft, Seattle, WA, USA) is gaining attention as a new motion detecting device that is nonintrusive and easy to implement. This study aimed to apply Kinect to measure shoulder ROM in AC; we evaluated its validity by calculating the agreement of the measurements obtained using Kinect with those obtained using goniometer and assessed its utility for the diagnosis of AC. Both shoulders of 15 healthy volunteers and affected shoulders of 12 patients with AC were included in the study. The passive and active ROM of each were measured with a goniometer for flexion, abduction, and external rotation. Their active shoulder motions for each direction were again captured using Kinect and the ROM values were calculated. The agreement between the two measurements was tested with the intraclass correlation coefficient (ICC). Diagnostic performance using the Kinect ROM was evaluated with Cohen’s kappa value. The cutoff values of the limited ROM were determined in the following ways: the same as passive ROM values, reflecting the mean difference, and based on receiver operating characteristic curves. The ICC for flexion/abduction/external rotation between goniometric passive ROM and the Kinect ROM were 0.906/0.942/0.911, while those between active ROMs and the Kinect ROMs were 0.864/0.932/0.925. Cohen’s kappa values were 0.88, 0.88, and 1.0 with the cutoff values in the order above. Measurements of the shoulder ROM using Kinect show excellent agreement with those taken using a goniometer. These results indicate that the Kinect can be used to measure shoulder ROM and to diagnose AC as an alternative to goniometer.  相似文献   
32.
In order to study the expression and role of transglutaminases in the formation of the cross-linked cell envelope of human epidermis, we have used a synthetic oligonucleotide encoding the consensual active site sequence of known transglutaminase sequences. By Northern blot analysis, newborn foreskin epidermis expresses three different mRNA species of about 3.7, 3.3, and 2.9 kilobases while normal cultured epidermal keratinocytes express only the 3.7- and 2.9-kilobase species. The largest species corresponds to a known ubiquitous tissue type II or transglutaminase C activity, the smallest corresponds to a known type I or transglutaminase K activity, and the mid-sized component apparently encodes a transglutaminase E activity that has recently been shown to be expressed in terminally differentiating epidermis (Kim, H. C., Lewis, M. S., Gorman, J. L., Park, S. C., Girard, J. E., Folk, J. E. & Chung, S. I. (1990) J. Biol. Chem., in press). Using the active site oligonucleotide as a probe, we have isolated and sequenced cDNA clones encoding the transglutaminase K enzyme. The deduced complete protein sequence has 813-amino acid residues of 89.3 kDa, has a pl of 5.7, and is likely to be an essentially globular protein, which are properties expected from the partially purified enzyme. It shares 49-53% sequence homology with the other transglutaminases of known sequence, especially in regions carboxyl-terminal to the active site, and possesses sequences likely to confer its Ca2+ dependence. Interestingly, its larger size is due to extended sequences on its amino and carboxyl termini, absent on the other transglutaminases, that may define its unique properties.  相似文献   
33.
88 rice and 75 soybean samples were collected from 8 provinces of Korea from March through September in 1988. The Fusarium mycotoxins, zearalenone was analyzed by direct competitive enzyme linked immunosorbent assay. 10.2% of rice and 9.3 % of soybean samples contained detectable zearalenone. The average levels of zearalenone of rice and soybean samples were 11.78μg/kg and 7.70μ/kg, respectively.  相似文献   
34.
Prostate cancer (PCa) is the second most common malignancy and is the fifth leading cause of cancer mortality among men globally. Docetaxel-based therapy remains the first-line treatment for metastatic castration-resistant prostate cancer. However, dose-limiting toxicity including neutropenia, myelosuppression and neurotoxicity is the major reason for docetaxel dose reductions and fewer cycles administered, despite a recent study showing a clear survival benefit with increased total number of docetaxel cycles in PCa patients. Although previous studies have attempted to improve the efficacy and reduce docetaxel toxicity through drug combination, no drug has yet demonstrated improved overall survival in clinical trial, highlighting the challenges of improving the activity of docetaxel monotherapy in PCa. Herein, we identified 15 lethality hits for which inhibition could enhance docetaxel sensitivity in PCa cells via a high-throughput kinome-wide loss-of-function screen. Further drug-gene interactions analyses identified Janus kinase 1 (JAK1) as a viable druggable target with existing experimental inhibitors and FDA-approved drugs. We demonstrated that depletion of endogenous JAK1 enhanced docetaxel-induced apoptosis in PCa cells. Furthermore, inhibition of JAK1/2 by baricitinib and ruxolitinib synergizes docetaxel sensitivity in both androgen receptor (AR)–negative DU145 and PC3 cells, but not in the AR-positive LNCaP cells. In contrast, no synergistic effects were observed in cells treated with JAK2-specific inhibitor, fedratinib, suggesting that the synergistic effects are mainly mediated through JAK1 inhibition. In conclusion, the combination therapy with JAK1 inhibitors and docetaxel could be a useful therapeutic strategy in the treatment of prostate cancers.  相似文献   
35.
Tumor cells that disseminate from the primary tumor and survive the vascular system can eventually extravasate across the endothelium to metastasize at a secondary site. In this study, we developed a microfluidic system to mimic tumor cell extravasation where cancer cells can transmigrate across an endothelial monolayer into a hydrogel that models the extracellular space. The experimental protocol is optimized to ensure the formation of an intact endothelium prior to the introduction of tumor cells and also to observe tumor cell extravasation by having a suitable tumor seeding density. Extravasation is observed for 38.8% of the tumor cells in contact with the endothelium within 1 day after their introduction. Permeability of the EC monolayer as measured by the diffusion of fluorescently-labeled dextran across the monolayer increased 3.8 fold 24 hours after introducing tumor cells, suggesting that the presence of tumor cells increases endothelial permeability. The percent of tumor cells extravasated remained nearly constant from1 to 3 days after tumor seeding, indicating extravasation in our system generally occurs within the first 24 hours of tumor cell contact with the endothelium.  相似文献   
36.
The whole plants of Carpesium genus are used in traditional medicine as anti-pyretic, analgesic and vermifugic, including a topical application for sores and inflammation. A previous study on Carpesium genus suggested that the antiplasmodial activity against Plasmodium falciparum was due to the existence of 11(13)- dehydroivaxillin (DDV) from EtOAc extracts of C. ceruum (Compositae). Here, the antimalarial activity of DDV was evaluated against Plasmodium berghei in mice. The LD50 of the compound was determined as 51.2 mg/kg, while doses of 124 mg/kg and above were found to be lethal to mice. DDV (2, 5, 10 mg/kg/day) exhibited a significant blood schizontocidal activity in 4-day early infection, repository evaluation and in an established infection with a significant mean survival time comparable to that of the standard drug, chloroquine, 5 mg/kg/day. DDV possesses a promising antiplasmodial activity, which can be exploited in malaria therapy.  相似文献   
37.
To delineate the temporal dynamics between alcohol tax policy changes and related health outcomes, this study examined the age, period and cohort effects on alcohol-related mortality in relation to changes in government alcohol policies. We used the age-period-cohort modeling to analyze retrospective mortality data over 30 years from 1981 to 2010 in a rapidly developed Chinese population, Hong Kong. Alcohol-related mortality from 1) chronic causes, 2) acute causes, 3) all (chronic+acute) causes and 4) causes 100% attributable to alcohol, as defined according to the Alcohol-Related Disease Impact (ARDI) criteria developed by the US Centers for Disease Control and Prevention, were examined. The findings illustrated the possible effects of alcohol policy changes on adult alcohol-related mortality. The age-standardized mortality trends were generally in decline, with fluctuations that coincided with the timing of the alcohol policy changes. The age-period-cohort analyses demonstrated possible temporal dynamics between alcohol policy changes and alcohol-related mortality through the period effects, and also generational impact of alcohol policy changes through the cohort effects. Based on the illustrated association between the dramatic increase of alcohol imports in the mid-1980s and the increased alcohol-related mortality risk of the generations coming of age of majority at that time, attention should be paid to generations coming of drinking age during the 2007–2008 duty reduction.  相似文献   
38.
Small ubiquitin-like modifier (SUMO), a member of the ubiquitin-related protein family, is covalently conjugated to lysine residues of its substrates in a process referred to as SUMOylation. SUMOylation occurs through a series of enzymatic reactions analogous to that of the ubiquitination pathway, resulting in modification of the biochemical and functional properties of substrates. To date, four mammalian SUMO isoforms, a single heterodimeric SUMO-activating E1 enzyme SAE1/SAE2, a single SUMO-conjugating E2 enzyme ubiquitin-conjugating enzyme E2I (UBC9), and a few subgroups of SUMO E3 ligases have been identified. Several SUMO E3 ligases such as topoisomerase I binding, arginine/serine-rich (TOPORS), TNF receptor-associated factor 7 (TRAF7), and tripartite motif containing 27 (TRIM27) have dual functions as ubiquitin E3 ligases. Here, we demonstrate that the ubiquitin E3 ligase UHRF2 also acts as a SUMO E3 ligase. UHRF2 effectively enhances zinc finger protein 131 (ZNF131) SUMOylation but does not enhance ZNF131 ubiquitination. In addition, the SUMO E3 activity of UHRF2 on ZNF131 depends on the presence of SET and RING finger-associated and nuclear localization signal-containing region domains, whereas the critical ubiquitin E3 activity RING domain is dispensable. Our findings suggest that UHRF2 has independent functional domains and regulatory mechanisms for these two distinct enzymatic activities.  相似文献   
39.
40.
Levansucrase of Zymomonas mobilis was immobilized onto the surface of hydroxyapatite by ionic binding. Optimum conditions for the immobilization were: pH 6.0, 4 h of immobilization reaction time, and 20 U of enzyme/g of matrix. The enzymatic and biochemical properties of the immobilized enzyme were similar to those of the native enzyme, especially towards the effect of salts and detergents. The immobilized enzyme showed sucrose hydrolysis activity higher as that of the native enzyme, but levan formation activity was 70% of the native enzyme. HPLC analysis of levan produced by immobilized enzyme showed the presence of two different types of levan: high-molecular-weight levan and low-molecular-weight levan. The proportion of low-molecular-weight levan to total levan produced by the immobilized enzyme was much higher than that with the native enzyme, indicating that immobilized levansucrase could be applied to produce low-molecular-weight levan. Immobilized levansucrase retained 65% of the original activity after 6 times of repeated uses and 67% of the initial activity after 40 d when stored at 4 °C.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号