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   5140篇
  免费   331篇
  国内免费   345篇
  5816篇
  2024年   10篇
  2023年   71篇
  2022年   158篇
  2021年   302篇
  2020年   215篇
  2019年   229篇
  2018年   186篇
  2017年   152篇
  2016年   231篇
  2015年   337篇
  2014年   366篇
  2013年   399篇
  2012年   531篇
  2011年   433篇
  2010年   256篇
  2009年   238篇
  2008年   254篇
  2007年   202篇
  2006年   183篇
  2005年   144篇
  2004年   113篇
  2003年   101篇
  2002年   103篇
  2001年   84篇
  2000年   76篇
  1999年   73篇
  1998年   42篇
  1997年   40篇
  1996年   35篇
  1995年   42篇
  1994年   39篇
  1993年   24篇
  1992年   30篇
  1991年   33篇
  1990年   17篇
  1989年   16篇
  1988年   12篇
  1987年   10篇
  1986年   7篇
  1985年   10篇
  1984年   3篇
  1983年   1篇
  1981年   3篇
  1980年   2篇
  1979年   2篇
  1965年   1篇
排序方式: 共有5816条查询结果,搜索用时 15 毫秒
101.
The aim of our meta-analysis was to quantitatively summarize the association of TYK2 gene polymorphisms with autoimmune and inflammatory diseases. 11 studies that included data from 21497 cases and 22647 controls were identified. OR was used as a measure of the effect of the association in a fixed/random effect model. Meta-analysis was performed for six TYK2 gene polymorphisms (rs34536443, rs2304256, rs280523, rs280519, rs12720270 and rs12720356). Significant association was found in rs34536443 (C versus G: OR = 0.76, 95% CI = 0.69–0.84, P < 0.00001; GC + CC versus GG: OR = 0.78, 95% CI = 0.68–0.90, P = 0.0005; CC versus GG + GC: OR = 0.76, 95% CI = 0.28–2.05, P = 0.58; CC versus GG: OR = 0.74, 95% CI = 0.27–2.02, P = 0.56; GC versus GG: OR = 0.78, 95% CI = 0.68–0.90, P = 0.0006) and rs2304256 (A versus C: OR = 0.78, 95% CI = 0.70–0.87, P < 0.0001; CA + AA versus CC: OR = 0.69, 95% CI = 0.59–0.81, P < 0.0001; AA versus CC + CA: OR = 0.75, 95% CI = 0.66–1.00, P = 0.05; AA versus CC: OR = 0.64, 95% CI = 0.47–0.86, P = 0.003; CA versus CC: OR = 0.70, 95% CI = 0.60–0.83, P < 0.0001) in TYK2 gene, but not for the other polymorphisms (rs280523, rs280519, rs12720270, and rs12720356). This meta-analysis demonstrates that autoimmune and inflammatory diseases is associated with TYK2 gene rs34536443 and rs2304256 polymorphisms, but not rs280523, rs280519, rs12720270 and rs12720356.  相似文献   
102.
Ponatinib (AP24534) was previously identified as a pan-BCR-ABL inhibitor that potently inhibits the T315I gatekeeper mutant, and has advanced into clinical development for the treatment of refractory or resistant CML. In this study, we explored a novel series of five and six membered monocycles as alternate hinge-binding templates to replace the 6,5-fused imidazopyridazine core of ponatinib. Like ponatinib, these monocycles are tethered to pendant toluanilides via an ethynyl linker. Several compounds in this series displayed excellent in vitro potency against both native BCR-ABL and the T315I mutant. Notably, a subset of inhibitors exhibited desirable PK and were orally active in a mouse model of T315I-driven CML.  相似文献   
103.
Hua Z  Zou C  Shiu SH  Vierstra RD 《PloS one》2011,6(1):e16219
The emergence of multigene families has been hypothesized as a major contributor to the evolution of complex traits and speciation. To help understand how such multigene families arose and diverged during plant evolution, we examined the phylogenetic relationships of F-Box (FBX) genes, one of the largest and most polymorphic superfamilies known in the plant kingdom. FBX proteins comprise the target recognition subunit of SCF-type ubiquitin-protein ligases, where they individually recruit specific substrates for ubiquitylation. Through the extensive analysis of 10,811 FBX loci from 18 plant species, ranging from the alga Chlamydomonas reinhardtii to numerous monocots and eudicots, we discovered strikingly diverse evolutionary histories. The number of FBX loci varies widely and appears independent of the growth habit and life cycle of land plants, with a little as 198 predicted for Carica papaya to as many as 1350 predicted for Arabidopsis lyrata. This number differs substantially even among closely related species, with evidence for extensive gains/losses. Despite this extraordinary inter-species variation, one subset of FBX genes was conserved among most species examined. Together with evidence of strong purifying selection and expression, the ligases synthesized from these conserved loci likely direct essential ubiquitylation events. Another subset was much more lineage specific, showed more relaxed purifying selection, and was enriched in loci with little or no evidence of expression, suggesting that they either control more limited, species-specific processes or arose from genomic drift and thus may provide reservoirs for evolutionary innovation. Numerous FBX loci were also predicted to be pseudogenes with their numbers tightly correlated with the total number of FBX genes in each species. Taken together, it appears that the FBX superfamily has independently undergone substantial birth/death in many plant lineages, with its size and rapid evolution potentially reflecting a central role for ubiquitylation in driving plant fitness.  相似文献   
104.
Chicken cystatin (cC) mutant I66Q is located in the hydrophobic core of the protein and increases the propensity for amyloid formation. Here, we demonstrate that under physiological conditions, the replacement of Ile with the Gln in the I66Q mutant increases the susceptibility for the disulfide bond Cys71–Cys81 to be reduced when compared to the wild type (WT) cC. Molecular dynamics (MD) simulations under conditions favoring cC amyloid fibril formation are in agreement with the experimental results. MD simulations were also performed to investigate the impact of disrupting the Cys71–Cys81 disulfide bond on the conformational stability of cC at the atomic level, and highlighted major disruption to the cC appendant structure. Domain swapping and extensive unfolding has been proposed as one of the possible mechanisms initiating amyloid fibril formation by cystatin. Our in silico studies suggest that disulfide bond formation between residues Cys95 and Cys115 is necessary to maintain conformational stability of the I66Q mutant following breakage of the Cys71–Cys81 disulfide bridge. Subsequent breakage of disulfide bond Cys95–Cys115 resulted in large structural destabilization of the I66Q mutant, which increased the α–β interface distance and expanded the hydrophobic core. These experimental and computational studies provide molecular-level insight into the relationship between disulfide bond formation and progressive unfolding of amyloidogenic cC mutant I66Q.

An animated Interactive 3D Complement (I3DC) is available in Proteopedia at http://proteopedia.org/w/Journal:JBSD:23  相似文献   
105.
Soft tissues are anisotropic materials yet a majority of mechanical property tests have been uniaxial, which often failed to recapitulate the tensile response in other directions. This paper aims to study the feasibility of determining material parameters of anisotropic tissues by uniaxial extension with a minimal loss of anisotropic information. We assumed that by preselecting a certain constitutive model, we could give the constitutive parameters based on uniaxial extension data from orthogonal strip samples. In our study, the Holzapfel–Weizsäcker type strain energy density function (H–W model) was used to determine the material parameters of arterial walls from two fresh donation bodies. The key points we applied were the relationships between strain components in uniaxial tensile tests and the methods of stochastic optimisation. Further numerical experiments were taken. The estimate–effect ratio, defined by the number of data with the precision of estimation less than 0.5% over whole size of data, was calculated to demonstrate the feasibility of our method. The material parameters for Chinese aorta and pulmonary artery were given with the maximum root mean square (RMS) errors 0.042, and the minimal estimate–effect ratio in numerical experiments was 90.79%. Our results suggest that the constitutive parameters of arterial walls can be determined from uniaxial extension data, given the passive mechanical behaviour governed by H–W model. This method may apply to other tissues using different constitutive models.  相似文献   
106.
Three nitrophenol isomer-imprinted polymers were prepared under the same conditions using 4-vinylpyridine as a functional monomer. Different recognition capacities for template molecules were observed for the three polymers. Another imprinting system with stronger acidity than nitrophenol isomers, 2-hydroxybenzoic acid (salicylic acid) and 4-hydroxybenzoic acid, was imprinted using 4-vinylpyridine or acrylamide as functional monomer respectively. Both 4-hydroxybenzoic acid-imprinted polymers using the two monomers showed recognition ability for the template molecule. However, when acrylamide was chosen as functional monomer, the salicylic acid-imprinted polymer showed very weak recognition for the template molecule, whereas strong recognition ability of the resultant polymer for salicylic acid was observed with 4-vinylpyridine as functional monomer. It seems that the structure and acidity of template molecules is responsible for the difference in recognition, by influencing the formation and strength of interaction between template molecule and functional monomer during the imprinting process. An understanding of the mechanism of molecular imprinting and molecular recognition of MIPs will help to predict the selectivity of MIPs on the basis of template molecule properties.  相似文献   
107.
108.
109.
110.

Objectives

China is facing the unprecedented challenge of rapidly increasing rural-to-urban migration. Migrants are in a vulnerable state when they attempt to access to primary care services. This study was designed to explore rural-to-urban migrants’ experiences in primary care, comparing their quality of primary care experiences under different types of medical institutions in Guangzhou, China.

Methods

The study employed a cross-sectional survey of 736 rural-to-urban migrants in Guangzhou, China in 2014. A validated Chinese version of Primary Care Assessment Tool—Adult Short Version (PCAT-AS), representing 10 primary care domains was used to collect information on migrants’ quality of primary care experiences. These domains include first contact (utilization), first contact (accessibility), ongoing care, coordination (referrals), coordination (information systems), comprehensiveness (services available), comprehensiveness (services provided), family-centeredness, community orientation and culturally competent. These measures were used to assess the quality of primary care performance as reported from patients’ perspective. Analysis of covariance was conducted for comparison on PCAT scores among migrants accessing primary care in tertiary hospitals, municipal hospitals, community health centers/community health stations, and township health centers/rural health stations. Multiple linear regression models were used to explore factors associated with PCAT total scores.

Results

After adjustments were made, migrants accessing primary care in tertiary hospitals (25.49) reported the highest PCAT total scores, followed by municipal hospitals (25.02), community health centers/community health stations (24.24), and township health centers/rural health stations (24.18). Tertiary hospital users reported significantly better performance in first contact (utilization), first contact (accessibility), coordination (information system), comprehensiveness (service available), and cultural competence. Community health center/community health station users reported significantly better experience in the community orientation domain. Township health center/rural health station users expressed significantly better experience in the ongoing care domain. There were no statistically significant differences across settings in the ongoing care, comprehensiveness (services provided), and family-centeredness domains. Multiple linear regression models showed that factors positively associated with higher PCAT total scores also included insurance covering parts of healthcare payment (P<0.001).

Conclusions

This study highlights the need for improvement in primary care provided by primary care institutions for rural-to-urban migrants. Relevant policies related to medical insurance should be implemented for providing affordable healthcare services for migrants accessing primary care.  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