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   2331篇
  免费   305篇
  国内免费   1篇
  2637篇
  2023年   12篇
  2022年   29篇
  2021年   55篇
  2020年   45篇
  2019年   35篇
  2018年   56篇
  2017年   42篇
  2016年   82篇
  2015年   130篇
  2014年   123篇
  2013年   128篇
  2012年   133篇
  2011年   114篇
  2010年   81篇
  2009年   87篇
  2008年   93篇
  2007年   132篇
  2006年   95篇
  2005年   86篇
  2004年   71篇
  2003年   67篇
  2002年   89篇
  2001年   75篇
  2000年   66篇
  1999年   62篇
  1998年   33篇
  1997年   30篇
  1996年   20篇
  1995年   19篇
  1994年   28篇
  1993年   12篇
  1992年   53篇
  1991年   36篇
  1990年   35篇
  1989年   43篇
  1988年   21篇
  1987年   30篇
  1986年   29篇
  1985年   26篇
  1984年   38篇
  1983年   22篇
  1982年   25篇
  1981年   17篇
  1979年   12篇
  1978年   18篇
  1977年   16篇
  1976年   8篇
  1975年   11篇
  1973年   14篇
  1970年   8篇
排序方式: 共有2637条查询结果,搜索用时 0 毫秒
71.
72.
BackgroundLarge variability in tests and differences in scoring systems used to study central coherence in eating disorders may lead to different interpretations, inconsistent findings and between study discrepancies. This study aimed to address inconsistencies by collating data from several studies from the same research group that used the Rey Osterrieth Complex Figure Test (Rey Figure) in order to produce norms to provide benchmark data for future studies.MethodData was collated from 984 participants in total. Anorexia Nervosa, Bulimia Nervosa, recovered Anorexia Nervosa, unaffected family members and healthy controls were compared using the Rey Figure.ResultsPoor global processing was observed across all current eating disorder sub-groups and in unaffected relatives. There was no difference in performance between recovered AN and HC groups.ConclusionsThis is the largest dataset reported in the literature and supports previous studies implicating poor global processing across eating disorders using the Rey Figure. It provides robust normative data useful for future studies.  相似文献   
73.
Effects of secretin and Cholecystokinin-Pancreozymin (CCK-PZ) on the secretion of bile in anaesthetized rabbits have been studied. Single injections of secretin (5.0 u.kg(-1) significantly increased the flow of bile irrespectively of whether the cystic duct was free or had been tied. A sustained increase in bile flow could be obtained by the continuous infusion of secretin. Cholecystokinin-Pancreozymin was effective in increasing the bile flow in doses of 1.0 u.kg(-1). Much of the effect could be attributed to contraction of the gallbladder but a significant increase in flow could still be elicited after ligation of the cystic duct. Our findings strongly suggest that the biliary secretion in rabbits is not as different from the general pattern as has previously been suggested.  相似文献   
74.
Yu X  Klejnot J  Zhao X  Shalitin D  Maymon M  Yang H  Lee J  Liu X  Lopez J  Lin C 《The Plant cell》2007,19(10):3146-3156
CRY2 is a blue light receptor regulating light inhibition of hypocotyl elongation and photoperiodic flowering in Arabidopsis thaliana. The CRY2 protein is found primarily in the nucleus, and it is known to undergo blue light-dependent phosphorylation and degradation. However, the subcellular location where CRY2 exerts its function or undergoes blue light-dependent phosphorylation and degradation remains unclear. In this study, we analyzed the function and regulation of conditionally nuclear-localized CRY2. Our results show that CRY2 mediates blue light inhibition of hypocotyl elongation and photoperiodic promotion of floral initiation in the nucleus. Consistent with this result and a hypothesis that blue light-dependent phosphorylation is associated with CRY2 function, we demonstrate that CRY2 undergoes blue light-dependent phosphorylation in the nucleus. CRY2 phosphorylation is required for blue light-dependent CRY2 degradation, but only a limited quantity of CRY2 is phosphorylated at any given moment in seedlings exposed to blue light, which explains why continuous blue light illumination is required for CRY2 degradation. Finally, we showed that CRY2 is ubiquitinated in response to blue light and that ubiquitinated CRY2 is degraded by the 26S proteasome in the nucleus. These findings demonstrate that a photoreceptor can complete its posttranslational life cycle (from protein modification, to function, to degradation) inside the nucleus.  相似文献   
75.

Background

Tick-borne relapsing fever spirochetes are maintained in endemic foci that involve a diversity of small mammals and argasid ticks in the genus Ornithodoros. Most epidemiological studies of tick-borne relapsing fever in West Africa caused by Borrelia crocidurae have been conducted in Senegal. The risk for humans to acquire relapsing fever in Mali is uncertain, as only a few human cases have been identified. Given the high incidence of malaria in Mali, and the potential to confuse the clinical diagnosis of these two diseases, we initiated studies to determine if there were endemic foci of relapsing fever spirochetes that could pose a risk for human infection.

Methodology/Principal Findings

We investigated 20 villages across southern Mali for the presence of relapsing fever spirochetes. Small mammals were captured, thin blood smears were examined microscopically for spirochetes, and serum samples were tested for antibodies to relapsing fever spirochetes. Ornithodoros sonrai ticks were collected and examined for spirochetal infection. In total, 11.0% of the 663 rodents and 14.3% of the 63 shrews tested were seropositive and 2.2% of the animals had active spirochete infections when captured. In the Bandiagara region, the prevalence of infection was higher with 35% of the animals seropositive and 10% infected. Here also Ornithodoros sonrai were abundant and 17.3% of 278 individual ticks tested were infected with Borrelia crocidurae. Fifteen isolates of B. crocidurae were established and characterized by multi-locus sequence typing.

Conclusions/Significance

The potential for human tick-borne relapsing fever exists in many areas of southern Mali.  相似文献   
76.
77.
We tested the effects among a purportedly sustainable water-soluble fertilizer, a conventional water-soluble fertilizer, an alternation of these, a controlled-release fertilizer, and a clear water control on the life-history traits of sweetpotato whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae; =Bemisia argentifolii Bellows & Perring) biotype B reared on poinsettia (Euphorbia pulcherrima Willdenow ex Klotzch). Free amino acids in petioles were measured to estimate plant nutrient assimilation and phloem nutritional quality for B. tabaci biotype B. The sustainable fertilizer produced plants with the highest concentration of amino acids. In contrast, fecundity of whiteflies was lowest in plants treated with the sustainable fertilizer and the water control. The relationship between total amino acids in phloem and survival was significantly quadratic, with the highest survival at intermediate levels. Fecundity, however, was negatively correlated with total amino acid content of the maternal host plant. Variation in total amino acid concentration in petioles of plants treated within fertilizer treatments makes it difficult to predict whether a particular fertilizer will produce plants with enough amino acids to deleteriously affect both survivorship and fecundity and yet yield a plant of good quality. Despite this limitation, we can conclude that the use of this sustainable fertilizer will not cause increases in whitefly populations relative to plants fertilized with water-soluble and slow-release fertilizers that deliver the same level of nitrogen to the plant.  相似文献   
78.
The first mutant of Streptococcus pneumoniae showing a complete deletion in the lytA gene coding for the N-acetylmuramyl-L-alanine amidase has been isolated and characterized. This amidase was previously the only autolysin detected in this species. This mutant shows a normal growth rate and can be transformed using either chromosomal or plasmid DNA. The most remarkable biological consequences of the absence of the amidase are the formation of small chains (six to eight cells) and the absence of lysis in the stationary phase of growth. In addition, this mutant exhibits a tolerant response against the beta-lactam antibiotics.  相似文献   
79.
The physiological role of topoisomerase III is unclear for any organism. We show here that the removal of topoisomerase III in temperature sensitive topoisomerase IV mutants in Escherichia coli results in inviability at the permissive temperature. The removal of topoisomerase III has no effect on the accumulation of catenated intermediates of DNA replication, even when topoisomerase IV activity is removed. Either recQ or recA null mutations, but not helD null or lexA3, partially rescued the synthetic lethality of the double topoisomerase III/IV mutant, indicating a role for topoisomerase III in recombination. We find a bias against deleting the gene encoding topoisomerase III in ruvC53 or DeltaruvABC backgrounds compared with the isogenic wild-type strains. The topoisomerase III RuvC double mutants that can be constructed are five- to 10-fold more sensitive to UV irradiation and mitomycin C treatment and are twofold less efficient in transduction efficiency than ruvC53 mutants. The overexpression of ruvABC allows the construction of the topoisomerase III/IV double mutant. These data are consistent with a role for topoisomerase III in disentangling recombination intermediates as an alternative to RuvABC to maintain the stability of the genome.  相似文献   
80.
Cryptococcus neoformans, the main causative agent of cryptococcosis, is a fungal pathogen that causes life‐threatening meningoencephalitis in immunocompromised patients. To date, there is no vaccine or immunotherapy approved to treat cryptococcosis. Cell‐ and antibody‐mediated immune responses collaborate to mediate optimal protection against C. neoformans infections. Accordingly, we identified cryptococcal protein fractions capable of stimulating cell‐ and antibody‐mediated immune responses and determined their efficacy to elicit protection against cryptococcosis. Proteins were extracted from C. neoformans and fractionated based on molecular mass. The fractions were then evaluated by immunoblot analysis for reactivity to serum extracted from protectively immunized mice and in cytokine recall assays for their efficacy to induce pro‐inflammatory and Th1‐type cytokine responses associated with protection. MS analysis revealed a number of proteins with roles in stress response, signal transduction, carbohydrate metabolism, amino acid synthesis, and protein synthesis. Immunization with select protein fractions containing immunodominant antigens induced significantly prolonged survival against experimental pulmonary cryptococcosis. Our studies support using the combination of immunological and proteomic approaches to identify proteins that elicit antigen‐specific antibody and Th1‐type cytokine responses. The immunodominant antigens that were discovered represent attractive candidates for the development of novel subunit vaccines for treatment and/or prevention of cryptococcosis.  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