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   1240篇
  免费   79篇
  1319篇
  2022年   8篇
  2021年   19篇
  2020年   13篇
  2019年   16篇
  2018年   12篇
  2017年   14篇
  2016年   33篇
  2015年   43篇
  2014年   52篇
  2013年   80篇
  2012年   77篇
  2011年   94篇
  2010年   68篇
  2009年   44篇
  2008年   82篇
  2007年   73篇
  2006年   60篇
  2005年   55篇
  2004年   64篇
  2003年   60篇
  2002年   59篇
  2001年   15篇
  2000年   13篇
  1999年   13篇
  1998年   18篇
  1997年   7篇
  1996年   11篇
  1995年   13篇
  1994年   7篇
  1993年   12篇
  1992年   8篇
  1991年   15篇
  1990年   9篇
  1989年   4篇
  1988年   5篇
  1987年   8篇
  1986年   14篇
  1985年   9篇
  1984年   13篇
  1983年   8篇
  1982年   11篇
  1981年   10篇
  1980年   13篇
  1979年   9篇
  1977年   9篇
  1976年   6篇
  1975年   7篇
  1974年   6篇
  1972年   3篇
  1946年   4篇
排序方式: 共有1319条查询结果,搜索用时 15 毫秒
61.
The sub-Antarctic waters of South Georgia Island (Islas Georgias del Sur, SG/IG) are a regularly visited feeding ground for southern right whales (Eubalaena australis, SRW) in the southwest Atlantic. Satellite telemetry and photo-identification records were compared to better understand the role of SG/IG in the SRW migratory network. We present the first insights from SRW satellite-tracked from the SG/IG feeding ground, habitat use patterns in the Scotia Arc, and movements to Antarctic habitats. Photo-identification comparisons to calving and feeding areas across the South Atlantic and a review of sightings of cetaceans reported from Bird Island (west of SG/IG) since 1979 illuminate long-term habitat use patterns in SG/IG. We present the first recorded migratory movement between SG/IG and multiple countries: Argentina, Uruguay, and Brazil. Photo-identification (1) linked SG/IG to a female SRW with a long-term sighting history in Brazil, and (2) provided the first match between SG/IG and the western Antarctic Peninsula, suggesting the latter could extend the feeding area for southwest Atlantic SRW. Satellite tracking and opportunistic sightings suggest that shelf and coastal waters west of SG/IG represent an important multi-season SRW feeding habitat and add to our overall understanding of habitats and ranges occupied by recovering southwest Atlantic SRW.  相似文献   
62.
The hepatitis C virus (HCV) NS3 protease is essential for polyprotein maturation and viral propagation, and it has been proposed as a suitable target for antiviral drug discovery. An N-terminal hexapeptide cleavage product of a dodecapeptide substrate identified as a weak competitive inhibitor of the NS3 protease activity was optimized to a potent and highly specific inhibitor of the enzyme. The effect of this potent NS3 protease inhibitor was evaluated on replication of subgenomic HCV RNA and compared with interferon-alpha (IFN-alpha), which is currently used in the treatment of HCV-infected patients. Treatment of replicon-containing cells with the NS3 protease inhibitor or IFN-alpha showed a dose-dependent decrease in subgenomic HCV RNA that reached undetectable levels following a 14-day treatment. Kinetic studies in the presence of either NS3 protease inhibitor or IFN-alpha also revealed similar profiles in HCV RNA decay with half-lives of 11 and 14 h, respectively. The finding that an antiviral specifically targeting the NS3 protease activity inhibits HCV RNA replication further validates the NS3 enzyme as a prime target for drug discovery and supports the development of NS3 protease inhibitors as a novel therapeutic approach for HCV infection.  相似文献   
63.
Abstract

During the 1970s, Thailand emerged as the major distant‐water fishing nation in Southeast Asia. By the 1980s, Thailand's neighboring states had introduced 200‐nautical‐mile economic zones with the consequence that the Thai fishing industry faces a loss of approximately 300,000 square kilometers of fishing grounds that had been utilized by the Thai trawler fleet. The Thai fishing industry will face a difficult time in the next decade as neighboring states take action to remove foreign vessels from their 200‐mile zones and the Thais are forced into their small zones in the Gulf of Thailand and Andaman Sea. Thailand, as a developing country with a distant‐water fishing fleet, is a victim of the 200‐mile economic zones.  相似文献   
64.
Cabozantinib is an inhibitor of multiple receptor tyrosine kinases, including MET and VEGFR2. In a phase II clinical trial in advanced prostate cancer (PCa), cabozantinib treatment improved bone scans in 68% of evaluable patients. Our studies aimed to determine the expression of cabozantinib targets during PCa progression and to evaluate its efficacy in hormone-sensitive and castration-resistant PCa in preclinical models while delineating its effects on tumor and bone. Using immunohistochemistry and tissue microarrays containing normal prostate, primary PCa, and soft tissue and bone metastases, our data show that levels of MET, P-MET, and VEGFR2 are increasing during PCa progression. Our data also show that the expression of cabozantinib targets are particularly pronounced in bone metastases. To evaluate cabozantinib efficacy on PCa growth in the bone environment and in soft tissues we used androgen-sensitive LuCaP 23.1 and castration-resistant C4-2B PCa tumors. In vivo, cabozantinib inhibited the growth of PCa in bone as well as growth of subcutaneous tumors. Furthermore, cabozantinib treatment attenuated the bone response to the tumor and resulted in increased normal bone volume. In summary, the expression pattern of cabozantinib targets in primary and castration-resistant metastatic PCa, and its efficacy in two different models of PCa suggest that this agent has a strong potential for the effective treatment of PCa at different stages of the disease.  相似文献   
65.
In this report we describe the synthesis and evaluation of diverse 4-arylproline analogs as HCV NS3 protease inhibitors. Introduction of this novel P2 moiety opened up new SAR and, in combination with a synthetic approach providing a versatile handle, allowed for efficient exploitation of this novel series of NS3 protease inhibitors. Multiple structural modifications of the aryl group at the 4-proline, guided by structural analysis, led to the identification of analogs which were very potent in both enzymatic and cell based assays. The impact of this systematic SAR on different drug properties is reported.  相似文献   
66.
Three polymorphisms of the glutamate decarboxylase 2 gene, which encodes the glutamic acid decarboxylase enzyme, have been associated with severe obesity in a large French cohort. One of these polymorphisms was shown to have functional consequences on promoter expression. Another polymorphism was associated with insulin levels and secretion. These associations were examined in 855 severely obese Utah subjects (mean BMI = 48 kg/m(2)) and a normal-weight and normoglycemic subset (N = 130, mean BMI = 22 kg/m(2)) of a random sample of the Utah population (N = 462). Comparisons of the normal-weight random group with the severely obese group did not result in significant genotype or allele frequency differences for any of the three polymorphisms, C61450A, T83897A, or A-243G (all p > or = 0.18). Haplotypes were also not related to severe obesity (p = 0.10). None of the polymorphisms was significantly related to fasting glucose, insulin levels, or homeostasis model assessment insulin resistance or secretion indices. This study of normal-weight and severely obese subjects from Utah does not provide evidence for involvement of the three genotyped polymorphisms in the glutamate decarboxylase 2 gene with obesity or with insulin- and glucose-related measures associated with obesity.  相似文献   
67.
Plants under attack by caterpillars emit volatile compounds that attract the herbivore’s natural enemies. In maize, the caterpillar-induced production of volatiles involves the phytohormone jasmonic acid (JA). In contrast, pathogen attack usually up-regulates the salicylic acid (SA)-pathway and results in systemic acquired resistance (SAR) against plant diseases. Activation of the SA-pathway has often been found to repress JA-dependent direct defenses, but little is known about the effects of SAR induction on indirect defenses such as volatile emission and parasitoid attraction. We examined if induction of SAR in maize, by chemical elicitation with the SA-mimic benzo-(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester (BTH), attenuates the emission of volatiles induced by Spodoptera littoralis or exogenously applied JA. In addition, we determined how these treatments affected the attractiveness of the plants to the parasitoid Microplitis rufiventris in a six-arm-olfactometer. BTH treatment alone resulted in significant systemic resistance of maize seedlings against the pathogen Setosphaeria turcica, but had no detectable effect on volatile emissions. Induction of SAR significantly reduced the emission rates of two compounds (indole and (E)-β-caryophyllene) in JA-treated plants, whereas no such negative cross-talk was found in caterpillar-damaged plants. Surprisingly, however, BTH treatment prior to caterpillar-feeding made the plants far more attractive to the parasitoid than plants that were only damaged by the herbivore. Control experiments showed that this response was due to plant-mediated effects rather than attractiveness of BTH itself. We conclude that in the studied system, plant protection by SAR activation is compatible with and can even enhance indirect defense against herbivores.  相似文献   
68.
In the past decades, many studies reported the presence of endoplasmic reticulum (ER)‐resident proteins in the cytosol. However, the mechanisms by which these proteins relocate and whether they exert cytosolic functions remain unknown. We find that a subset of ER luminal proteins accumulates in the cytosol of glioblastoma cells isolated from mouse and human tumors. In cultured cells, ER protein reflux to the cytosol occurs upon ER proteostasis perturbation. Using the ER luminal protein anterior gradient 2 (AGR2) as a proof of concept, we tested whether the refluxed proteins gain new functions in the cytosol. We find that refluxed, cytosolic AGR2 binds and inhibits the tumor suppressor p53. These data suggest that ER reflux constitutes an ER surveillance mechanism to relieve the ER from its contents upon stress, providing a selective advantage to tumor cells through gain‐of‐cytosolic functions—a phenomenon we name ER to Cytosol Signaling (ERCYS).  相似文献   
69.
TH17 cells enter tissues to facilitate pathogenic autoimmune responses, including multiple sclerosis (MS). However, the adhesion molecules involved in the unique migratory capacity of TH17 cells, into both inflamed and uninflamed tissues remain unclear. Herein, we characterize MCAM (CD146) as an adhesion molecule that defines human TH17 cells in the circulation; following in vitro restimulation of human memory T cells, nearly all of the capacity to secrete IL-17 is contained within the population of cells expressing MCAM. Furthermore, we identify the MCAM ligand as laminin 411, an isoform of laminin expressed within the vascular endothelial basement membranes under inflammatory as well as homeotstatic conditions. Purified MCAM-Fc binds to laminin 411 with an affinity of 27 nM, and recognizes vascular basement membranes in mouse and human tissue. MCAM-Fc binding was undetectable in tissue from mice with targeted deletion of laminin 411, indicating that laminin 411 is a major tissue ligand for MCAM. An anti-MCAM monoclonal antibody, selected for inhibition of laminin binding, as well as soluble MCAM-Fc, inhibited T cell adhesion to laminin 411 in vitro. When administered in vivo, the antibody reduced TH17 cell infiltration into the CNS and ameliorated disease in an animal model of MS. Our data suggest that MCAM and laminin 411 interact to facilitate TH17 cell entry into tissues and promote inflammation.  相似文献   
70.
Catecholaminergic neurons are affected in several neurological and psychiatric diseases. Tyrosine hydroxylase (TH) is the first, rate-limiting enzyme in catecholamine synthesis. We report a knockin mouse expressing Cre-recombinase from the 3'-untranslated region of the endogenous Th gene by means of an internal ribosomal entry sequence (IRES). The resulting Cre expression matches the normal pattern of TH expression, while the pattern and level of TH are not altered in the knockin mouse. Crossings with two different LacZ reporter mice demonstrated Cre-mediated genomic recombination in TH expressing tissues. In addition, LacZ was found in some unexpected cell populations (including oocytes), indicating recombination due to transient developmental TH expression. Our novel knockin mouse can be used for generation of tissue-specific or general knockouts (depending on scheme of crossing) in mice carrying genes flanked by loxP sites. This knockin mouse can also be used for tracing cell lineages expressing TH during development.  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