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   18704篇
  免费   1238篇
  国内免费   6篇
  19948篇
  2023年   179篇
  2022年   339篇
  2021年   612篇
  2020年   450篇
  2019年   577篇
  2018年   698篇
  2017年   607篇
  2016年   812篇
  2015年   1075篇
  2014年   1168篇
  2013年   1334篇
  2012年   1461篇
  2011年   1368篇
  2010年   817篇
  2009年   744篇
  2008年   875篇
  2007年   868篇
  2006年   786篇
  2005年   661篇
  2004年   605篇
  2003年   549篇
  2002年   466篇
  2001年   346篇
  2000年   312篇
  1999年   254篇
  1998年   114篇
  1997年   98篇
  1996年   82篇
  1995年   79篇
  1994年   77篇
  1993年   65篇
  1992年   133篇
  1991年   106篇
  1990年   74篇
  1989年   97篇
  1988年   81篇
  1987年   100篇
  1986年   91篇
  1985年   71篇
  1984年   69篇
  1983年   48篇
  1982年   39篇
  1981年   46篇
  1980年   29篇
  1979年   59篇
  1978年   37篇
  1976年   34篇
  1975年   40篇
  1974年   33篇
  1973年   48篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
Journal of Physiology and Biochemistry - Aerobic exercise training induces a unique cardioprotective phenotype, but it is becoming clear that it does not promote the same structural, functional,...  相似文献   
192.

Upper limb nerve injuries are common, and their treatment poses a challenge for physicians and surgeons. Experimental models help in minimum exploration of the functional characteristics of peripheral nerve injuries of forelimbs. This study was conducted to characterize the functional recovery (1, 3, 7, 10, 14, and 21 days) after median and ulnar nerve crush in mice and analyze the histological and biochemical markers of nerve regeneration (after 21 days). Sensory–functional impairments appeared after 1 day. The peripheral nerve morphology, the nerve structure, and the density of myelin proteins [myelin protein zero (P0) and peripheral myelin protein 22 (PMP22)] were analyzed after 21 days. Cold allodynia and fine motor coordination recovery occurred on the 10th day, and grip strength recovery was observed on the 14th day after injury. After 21 days, there was partial myelin sheath recovery. PMP22 recovery was complete, whereas P0 recovery was not. Results suggest that there is complete functional recovery even with partial remyelination of median and ulnar nerves in mice.

  相似文献   
193.
Dinotefuran is a low-cost agrochemical considered a highly toxic product. In this sense, there is a need for its constant environmental, biological, and food control, aiming to ensure its use to humans as well as to preserve biodiversity and ecosystems. In the present work, we developed an experimental and theoretical method for dinotefuran chiral discrimination. According to the main results, the dinotefuran enantioselective separation was efficiently optimized by high-performance liquid chromatography evaluating the influence of different percentage compositions in the mobile phase to improve the resolution of the peaks in the chromatogram. The novelty of this work was the proposition of a reduced molecular model for the chiral selector amylose-Tris-(3,5-dimethylphenylcarbamate) polysaccharide that was able to adequately describe at the molecular level its interaction with the dinotefuran enantiomers. Besides, the thermodynamic and structural parameters obtained via density functional theory calculations pointed out the chiral discrimination as well as the enantiomeric elution order of the analyte studied, confirming the experimental data, thus validating our proposed method. Finally, hydrogen bonds and repulsive interactions played a key role in the discrimination between the diastereomeric complexes, and consequently, for the dinotefuran enantioselective separation.  相似文献   
194.
BackgroundThis study evaluates an active search strategy for leprosy diagnosis based on responses to a Leprosy Suspicion Questionnaire (LSQ), and analyzing the clinical, immunoepidemiological and follow-up aspects for individuals living in a prison population.MethodsA cross-sectional study based on a questionnaire posing 14 questions about leprosy symptoms and signs that was distributed to 1,400 prisoners. This was followed by dermatoneurological examination, anti-PGL-I serology and RLEP-PCR. Those without leprosy were placed in the Non-leprosy Group (NLG, n = 1,216) and those diagnosed with clinical symptoms of leprosy were placed in the Leprosy Group (LG, n = 34).FindingsIn total, 896 LSQ were returned (64%), and 187 (20.9%) of the responses were deemed as positive for signs/symptoms, answering 2.7 questions on average. Clinically, 1,250 (89.3%) of the prisoners were evaluated resulting in the diagnosis of 34 new cases (LG), based on well-accepted clinical signs and symptoms, a new case detection rate of 2.7% within this population, while the NLG were comprised of 1,216 individuals. The confinement time medians were 39 months in the LG while it was 36 months in the NLG (p>0.05). The 31 leprosy cases who responded to the questionnaire (LSQ+) had an average of 1.5 responses. The symptoms “anesthetized skin area” and “pain in nerves” were most commonly mentioned in the LG while “tingling, numbness in the hands/feet”, “sensation of pricks and needles”, “pain in nerves” and “spots on the skin” responses were found in more than 30% of questionnaires in the NLG. Clinically, 88.2% had dysesthetic macular skin lesions and 97.1% presented some peripheral nerve impairment, 71.9% with some degree of disability. All cases were multibacillary, confirming a late diagnosis. Anti-PGL-I results in the LG were higher than in the NLG (p<0.0001), while the RLEP-PCR was positive in 11.8% of the patients.InterpretationOur findings within the penitentiary demonstrated a hidden prevalence of leprosy, although the individuals diagnosed were likely infected while living in their former communities and not as a result of exposure in the prison. The LSQ proved to be an important screening tool to help identify leprosy cases in prisons.  相似文献   
195.
Biological Trace Element Research - Excessive adipose tissue promotes the manifestation of endocrine disorders such as reduction of the secretion of zinc-α2-glycoprotein (ZAG), an adipokine...  相似文献   
196.
The study was undertaken to evaluate changes in the activity of adenosine deaminase (ADA) in brains of rats infected by Trypanosoma evansi. Each rat was intraperitoneally infected with 106 trypomastigotes either suspended in fresh (group A; n = 13) and cryopreserved blood (group B; n = 13). Thirteen animals were used as control (group C). ADA activity was estimated in the cerebellum, cerebral cortex, striatum and hippocampus. No differences (P > 0.05) in ADA activity were observed in the cerebellum between infected and non-infected animals. Significant (P < 0.05) reductions in ADA activity occurred in cerebral cortex in acutely (day 4 post-infection; PI) and chronically (day 20 PI) infected rats. ADA activity was significantly (P < 0.05) decreased in the hippocampus in acutely infected rats, but significantly (P < 0.05) increased in the chronically infected rats. Significant (P < 0.05) reductions in ADA activity occurred in the striatum of chronically infected rats. Parasites could be found in peripheral blood and brain tissue through microscopic examination and PCR assay, respectively, in acutely and chronically infected rats. The reduction of ADA activity in the brain was associated with high levels of parasitemia and anemia in acute infections. Alterations in ADA activity of the brain in T. evansi-infected rats may have implications for pathogenesis of the disease.  相似文献   
197.
Rhodococcus equi is a major cause of foal pneumonia and an opportunistic pathogen in immunocompromised humans. While alveolar macrophages constitute the primary replicative niche for R. equi, little is known about how intracellular R. equi is sensed by macrophages. Here, we discovered that in addition to previously characterized pro-inflammatory cytokines (e.g., Tnfa, Il6, Il1b), macrophages infected with R. equi induce a robust type I IFN response, including Ifnb and interferon-stimulated genes (ISGs), similar to the evolutionarily related pathogen, Mycobacterium tuberculosis. Follow up studies using a combination of mammalian and bacterial genetics demonstrated that induction of this type I IFN expression program is largely dependent on the cGAS/STING/TBK1 axis of the cytosolic DNA sensing pathway, suggesting that R. equi perturbs the phagosomal membrane and causes DNA release into the cytosol following phagocytosis. Consistent with this, we found that a population of ~12% of R. equi phagosomes recruits the galectin-3,-8 and -9 danger receptors. Interestingly, neither phagosomal damage nor induction of type I IFN require the R. equi’s virulence-associated plasmid. Importantly, R. equi infection of both mice and foals stimulates ISG expression, in organs (mice) and circulating monocytes (foals). By demonstrating that R. equi activates cytosolic DNA sensing in macrophages and elicits type I IFN responses in animal models, our work provides novel insights into how R. equi engages the innate immune system and furthers our understanding how this zoonotic pathogen causes inflammation and disease.  相似文献   
198.
Epithelial ovarian cancer is highly angiogenic and high expression of Nerve Growth Factor (NGF), a proangiogenic protein. Calreticulin is a multifunctional protein with anti-angiogenic properties and its translocation to the tumor cell membrane promotes recognition and engulfment by dendritic cells. The aim of this work was to evaluate calreticulin expression in human normal ovaries, benign and borderline tumors, and epithelial ovarian cancer samples and to evaluate whether NGF regulates calreticulin expression in human ovarian surface epithelium and in epithelial ovarian cancer cell lines. Calreticulin mRNA and protein levels were analyzed using RT-PCR, Western blot and immunohistochemistry in 67 human ovarian samples obtained from our Institution. Calreticulin expression induced by NGF stimulation in cell lines was evaluated using RT-PCR, Western blot and immunocytochemistry. We found a significant increase of calreticulin mRNA levels in epithelial ovarian cancer samples as compared to normal ovaries, benign tumors, and borderline tumors. Calreticulin protein levels, evaluated by Western blot, were also increased in epithelial ovarian cancer with respect to benign and borderline tumors. When HOSE and A2780 cell lines were stimulated with Nerve Growth Factor, we found an increase in calreticulin protein levels compared to controls. This effect was reverted by GW441756, a TRKA specific inhibitor. These results suggest that NGF regulates calreticulin protein levels in epithelial ovarian cells through TRKA receptor activation.  相似文献   
199.
Trichoderma harzianum ALL42 were capable of overgrowing and degrading Rhizoctonia solani and Macrophomina phaseolina mycelia, coiling around the hyphae with formation of apressoria and hook-like structures. Hyphae of T. harzianum ALL42 did not show any coiling around Fusarium sp. hyphae suggesting that mycoparasitism may be different among the plant pathogens. In this study, a secretome analysis was used to identify some extracellular proteins secreted by T. harzianum ALL42 after growth on cell wall of M. phaseolina, Fusarium sp., and R. solani. The secreted proteins were analyzed by two-dimensional electrophoresis and MALDI-TOF mass spectrometry. A total of 60 T. harzianum ALL42 secreted proteins excised from the gel were analyzed from the three growth conditions. While seven cell wall-induced proteins were identified, more than 53 proteins spots remain unidentified, indicating that these proteins are either novel proteins or proteins that have not yet been sequenced. Endochitinase, β-glucosidase, α-mannosidase, acid phosphatase, α-1,3-glucanase, and proteases were identified in the gel and also detected in the supernatant of culture.  相似文献   
200.
The sunbittern (Eurypyga helias) is a South American Gruiformes, the only member of Family Eurypigidae. In most phylogenetic proposals, it is placed in a more distant position than other families of the so-called “core Gruiformes”. Different studies based on molecular, morphological and biogeographical data suggest that the Eurypigidae is closely related to the kagu (Rhynochetos jubatus), the only species in Rynochetidae, another family not included in the core Gruiformes. Here, the karyotype of the sunbittern is described for the first time, by classical and molecular cytogenetics, using whole chromosome probes derived from Gallus gallus and Leucopternis albicollis. We found a diploid number of 80, with only one pair of biarmed autosomal macrochromosomes, similar to that observed in the kagu. Chromosome painting revealed that most syntenies found in the avian putative ancestral karyotype (PAK) were conserved in the sunbittern. However, PAK1, PAK2, and PAK5 corresponded to two chromosome pairs each. Probes derived from L. albicollis confirm that fissions in PAK1 and PAK2 were centric, whereas in PAK5 the fission is interstitial. In addition, there is fusion of segments homologous to PAK2q and PAK5. From a phylogenetic point of view, comparisons of our results with two other Gruiformes belonging to family Rallidae suggest that the PAK5q fission might be a synapomorphy for Gruiformes. Fissions in PAK1 and PAK2 are found only in Eurypigidae, and might also occur in Rynochetidae, in view of the similar chromosomal morphology between the sunbittern and the kagu. This suggests a close phylogenetic relationship between Eurypigidae and Rynochetidae, whose common ancestor was separated by the Gondwana vicariancy in South America and New Caledonia, respectively.  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