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   1220篇
  免费   97篇
  国内免费   4篇
  2023年   5篇
  2022年   7篇
  2021年   22篇
  2020年   13篇
  2019年   17篇
  2018年   31篇
  2017年   29篇
  2016年   42篇
  2015年   65篇
  2014年   49篇
  2013年   81篇
  2012年   91篇
  2011年   90篇
  2010年   58篇
  2009年   50篇
  2008年   76篇
  2007年   68篇
  2006年   69篇
  2005年   41篇
  2004年   38篇
  2003年   37篇
  2002年   33篇
  2001年   12篇
  2000年   30篇
  1999年   20篇
  1998年   10篇
  1997年   8篇
  1996年   8篇
  1995年   6篇
  1994年   12篇
  1992年   14篇
  1991年   12篇
  1990年   13篇
  1989年   9篇
  1988年   7篇
  1987年   11篇
  1986年   11篇
  1985年   7篇
  1984年   7篇
  1983年   9篇
  1982年   8篇
  1980年   12篇
  1978年   6篇
  1977年   7篇
  1976年   7篇
  1974年   6篇
  1972年   8篇
  1971年   6篇
  1968年   4篇
  1967年   4篇
排序方式: 共有1321条查询结果,搜索用时 187 毫秒
91.
92.
Endometrial secretions in the uterine cavity contain mediators important for endometrial receptivity and embryo implantation. Unbiased analysis of uterine fluid from a receptive versus nonreceptive time of the menstrual cycle and in fertile and infertile women will provide new insights into uterine receptivity. We hypothesized that proteomic analysis of human uterine lavages would identify proteins important for the establishment of pregnancy in humans. Lavages collected from fertile (n = 7) and infertile (n = 8) women during the midsecretory (MS) phase, and from fertile women during the midproliferative (MP) (n = 7) phase, were assessed using 2D-differential in gel electrophoresis (2D-DiGE) over a pI 4-7 range. Statistical analysis revealed 7 spots that were significantly decreased in the MP compared to the MS phase, while 18 spots showed differential expression between fertile and infertile women. A number of proteins were identified by mass spectrometry, including antithrombin III and alpha-2-macroglobulin, whose production was confirmed in endometrial epithelium. Their staining pattern suggests roles during embryo implantation. Assessment of the human endometrial secretome has identified differences in the protein content of uterine fluid with respect to receptivity and fertility.  相似文献   
93.
Cytokinins are a class of plant hormones that regulate the cell cycle and diverse developmental and physiological processes. Several compounds have been identified that antagonize the effects of cytokinins. Based on structural similarities and competitive inhibition, it has been assumed that these anticytokinins act through a common cellular target, namely the cytokinin receptor. Here, we examined directly the possibility that various representative classical anticytokinins inhibit the Arabidopsis cytokinin receptors CRE1/AHK4 (cytokinin response 1/Arabidopsis histidine kinase 4) and AHK3 (Arabidopsis histidine kinase 3). We show that pyrrolo[2,3-d]pyrimidine and pyrazolo[4,3-d]pyrimidine anticytokinins do not act as competitors of cytokinins at the receptor level. Flow cytometry and microscopic analyses revealed that anticytokinins inhibit the cell cycle and cause disorganization of the microtubular cytoskeleton and apoptosis. This is consistent with the hypothesis that they inhibit regulatory cyclin-dependent kinase (CDK) enzymes. Biochemical studies demonstrated inhibition by selected anti-cytokinins of both Arabidopsis and human CDKs. X-ray determination of the crystal structure of a human CDK2-anticytokinin complex demonstrated that the antagonist occupies the ATP-binding site of CDK2. Finally, treatment of human cancer cell lines with anticytokinins demonstrated their ability to kill human cells with similar effectiveness as known CDK inhibitors.  相似文献   
94.
Young adult male Wistar rats were treated, by gavage, with 80 or 320 mg/kg Pb2+ (lead acetate), 0.4 or 1.6 mg/kg Hg2+ (mercuric chloride) or both by combining the lower doses. For combination with alcohol, ethanol was added to the rats' drinking water in 5 v/v %. After 12 weeks of treatment, electrophysiological recording was made from the somatosensory cortex in urethane anaesthesia. Evoked potentials obtained by stimulation of the whiskers were recorded. Both metals, and alcohol alone, increased significantly the latency of the evoked response. Alcohol seemed to abolish the effect of Pb, but not of Hg. Fatigue, calculated form the response amplitude, was increased by Pb and Hg treatment and this effect of Hg was reduced by ethanol. Evoked activity and its dynamic characteristics were sensitive to the complex neurotoxic effect induced in the rats and can provide a basis for developing functional markers.  相似文献   
95.
The rice frog (Fejervarya limnocharis) species complex is widely distributed, from India to Japan, and most prevalently in Southeast Asia. Conspicuous morphological variation has been reported for this species complex throughout its distribution range. In the present study, we used mtDNA gene sequence and allozyme analyses to infer evolutionary affinities within this species complex using eight populations (Sri Lanka; Bangkok and Ranong in Thailand; Taiwan; and Hiroshima, Okinawa, Ishigaki and Iriomote in Japan). We also conducted crossing experiments among four populations from Japan, Thailand, and Sri Lanka in order to find out more about the reproductive isolating mechanisms that might exist among the East, Southeast, and South Asian populations of this species complex. The crossing experiments revealed that the Sri Lanka population is reproductively isolated from the Hiroshima, Bangkok, and Ranong populations by complete hybrid inviability, and that the Bangkok population may be reproductively isolated from the Hiroshima population by partial hybrid inviability. Thus, it is not unreasonable to regard the Sri Lanka population as a species separated from F. limnocharis. The mtDNA and allozyme data showed that the Ranong population is most closely related to the Bangkok population in nuclear genome, but more similar to the Okinawa and Taiwan populations in mtDNA genome. The present, preliminary survey may raise questions about the species status of these particular populations and also about the nature of the biological species concept.  相似文献   
96.
SHBG (sex hormone-binding globulin) is a transport protein specific for dihydrotestosterone, testosterone and estradiol. The missense mutation in exon 8 (GAC-->AAC) causing the amino acid exchange Asp-->Asn in codon 327 (D327N) correlates according to the published data with increased SHBG levels. We studied possible association of this polymorphism with polycystic ovary syndrome (PCOS) and anthropometric and biochemical parameters in 248 PCOS patients and 109 healthy control women. The D327N polymorphism (wild-type and variant allele) was detected using PCR-RFLP method (restriction enzyme Bbs-I). For statistical evaluation chi(2) test, Mann-Whitney test, ANCOVA, ANOVA (NCSS 2004, Statgraphics Plus v.5.1, USA) were used. There was no significant difference in genotype distribution between PCOS and controls (chi(2)=1.03, p=0.59). Moreover, we did not find an association of the variant allele with plasma SHBG level, steroid hormones, or screened parameters of lipid and glucose metabolism. In conclusion, the D327N polymorphism of the SHBG gene does not influence susceptibility to PCOS.  相似文献   
97.
98.
Hydrobiologia - To understand the spatiotemporal overlap in the habitat use of sympatric predators, we studied longitudinal activity and reservoir section and depth use of pike (Esox lucius),...  相似文献   
99.
Saccharomyces cerevisiae has recently been engineered to use acetate, a primary inhibitor in lignocellulosic hydrolysates, as a cosubstrate during anaerobic ethanolic fermentation. However, the original metabolic pathway devised to convert acetate to ethanol uses NADH-specific acetylating acetaldehyde dehydrogenase and alcohol dehydrogenase and quickly becomes constrained by limited NADH availability, even when glycerol formation is abolished. We present alcohol dehydrogenase as a novel target for anaerobic redox engineering of S. cerevisiae. Introduction of an NADPH-specific alcohol dehydrogenase (NADPH-ADH) not only reduces the NADH demand of the acetate-to-ethanol pathway but also allows the cell to effectively exchange NADPH for NADH during sugar fermentation. Unlike NADH, NADPH can be freely generated under anoxic conditions, via the oxidative pentose phosphate pathway. We show that an industrial bioethanol strain engineered with the original pathway (expressing acetylating acetaldehyde dehydrogenase from Bifidobacterium adolescentis and with deletions of glycerol-3-phosphate dehydrogenase genes GPD1 and GPD2) consumed 1.9 g liter−1 acetate during fermentation of 114 g liter−1 glucose. Combined with a decrease in glycerol production from 4.0 to 0.1 g liter−1, this increased the ethanol yield by 4% over that for the wild type. We provide evidence that acetate consumption in this strain is indeed limited by NADH availability. By introducing an NADPH-ADH from Entamoeba histolytica and with overexpression of ACS2 and ZWF1, we increased acetate consumption to 5.3 g liter−1 and raised the ethanol yield to 7% above the wild-type level.  相似文献   
100.
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