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   783篇
  免费   67篇
  国内免费   22篇
  2024年   2篇
  2023年   18篇
  2022年   22篇
  2021年   26篇
  2020年   21篇
  2019年   32篇
  2018年   49篇
  2017年   23篇
  2016年   22篇
  2015年   31篇
  2014年   32篇
  2013年   76篇
  2012年   40篇
  2011年   69篇
  2010年   27篇
  2009年   37篇
  2008年   37篇
  2007年   33篇
  2006年   25篇
  2005年   19篇
  2004年   14篇
  2003年   24篇
  2002年   23篇
  2001年   8篇
  2000年   11篇
  1999年   2篇
  1998年   4篇
  1997年   7篇
  1996年   5篇
  1995年   5篇
  1994年   12篇
  1993年   6篇
  1992年   5篇
  1991年   4篇
  1990年   6篇
  1987年   1篇
  1986年   1篇
  1985年   9篇
  1984年   11篇
  1983年   9篇
  1982年   14篇
  1981年   9篇
  1980年   13篇
  1979年   6篇
  1978年   5篇
  1977年   2篇
  1976年   3篇
  1975年   6篇
  1974年   1篇
  1973年   3篇
排序方式: 共有872条查询结果,搜索用时 15 毫秒
1.
G E Hoffman 《Peptides》1985,6(3):439-461
A wealth of evidence suggests that catecholamines (particularly norepinephrine) influence gonadotropin secretion via a direct interaction with the LHRH neurons. Neuropeptides such as neurotensin (NT) and substance P (SP) are likewise implicated in the control of LHRH secretion, based on pharmacological and preliminary anatomical studies. Since sub-populations of LHRH neurons project to areas of the brain other than the median eminence, a detailed analysis of the topography of axonal interactions of catecholamines (CA), substance P and neurotensin with LHRH cells was conducted in adult male mice using dual immunocytochemical techniques. An analysis of the patterns of apparent contact of NT or SP axons on LHRH cells as determined by close apposition of immunoreactive axons to LHRH cells when viewed under a light microscope at high magnification revealed that the density of NT or SP axons was not a reliable index of the degree of contact; in many locations, NT and SP had similar densities yet a greater portion of the LHRH cells appeared contacted by SP than NT. NT axons were in close contact with up to one-third of the LHRH cells. Analysis of the location of these "contacted" cells did not reveal a discrete subnucleus controlled by NT. Rather, the NT-contacted cells were scattered throughout the LHRH cell field. Interactions of LHRH cells with SP axons were likewise uniform throughout most of the LHRH cell field, with the exception of the most anterior portion of the field. In the anterior septum, few SP axons appeared to contact LHRH cells. Elsewhere, most of the LHRH cells were in contact with SP axons. For the CAs, the fiber density in the regions of the LHRH cells was uniformly moderate, yet the pattern of cells contacted showed variation across the LHRH cell field, with most of the "contacted" cells located near the OVLT and medial preoptic area. These data suggest that LHRH cells may be differentially regulated by NT, SP and the CAs.  相似文献   
2.
The use of five cholesterol ester hydrolases (CEH), numbered 1 to 5, for the enzymatic determination of total cholesterol of human and rat serum are compared. All CEH gave approximately the same value (no statistical difference) for human serum. However, when rat serum cholesterol was determined, CEH-2 yielded a value significantly lower when compared to the four other CEH. The ability of each CEH to hydrolyze individual cholesterol esters was tested. During a 15-min incubation, all CEH were capable of hydrolyzing nearly 100% of cholesteryl oleate and linoleate. In contrast, the hydrolysis of cholesteryl arachidonate was only partial and varied from 20 to 80% depending on the CEH used. The highest hydrolysis was obtained by CEH-1 while the value given by CEH-2 was only 22% of that obtained by CEH-1. The rate of hydrolysis of cholesteryl arachidonate differed markedly among the CEH. The CEH-2-hydrolyzed the cholesteryl arachidonate at a rate seven times lower than the rate obtained with CEH-1. The data suggest that, Under our incubation conditions, CEH-2 did not properly hydrolyze the cholesteryl arachidonate. This phenomenon may be crucial whenever total cholesterol has to be determined enzymatically in the serum of species that contain large amount of cholesteryl arachidonate such as rat, mouse, or dog serum.  相似文献   
3.
Two electroejaculators were used to collect semen from 40 adult male coyotes. The most effective apparatus used a two-ring rectal probe and an AC voltage of 18 (Vrms) at 1000 Hz. With this ejaculator, 11 of 15 coyotes produced a satisfactory semen sample, which averaged 0.9 ml in volume and 70 million spermatozoa per ml.  相似文献   
4.
Peripheral blood lymphocytes from ten human neonates and ten adults were studied. Many more medium and large cells were identified in neonates, and the ultrastructure of the medium-sized lymphocytes resembled guinea pig transitional cells. There were 20 times more nucleoside-incorporating lymphocytes in the newborn samples, and a neonatal high-labeling cell was identified.  相似文献   
5.
The CA1 pyramidal cells appear damaged in micrographs of guinea pig hippocampal slices incubated in normal physiological buffer at 36–37°C. This is remedied if slices are incubated in modified buffers for the first 45 min. Cell morphology is improved if this buffer is devoid of added Ca2+ and much improved if it contains N-methyl-D-aspartate (NMDA) receptor antagonists or 0 mM Ca2+ and 10 mM Mg2+. The cells then appear similar to CA1 pyramidal cells in situ. These findings support the notion that NMDA receptor activation and Ca2+, acting in the period immediately after slice preparation, permanently damage CA1 pyramidal cells in vitro.  相似文献   
6.
7.
The induction of long-term potentiation (LTP) is generally assumed to be triggered by Ca2+ entry into dendritic spines via NMDA receptor-gated channels. A previous computational model proposed that spines serve several functions in this process. First, they compartmentalize and amplify increases in [Ca2+]i. Second, they augment the nonlinear relationship between synaptic strength and the probability or magnitude of LTP induction. Third, they isolate the metabolic machinery responsible for LTP induction from increases in [Ca2+]i produced by voltage-gated Ca2+ channels in the dendritic shaft. Here we examine this last prediction of the model using methods that combine confocal microscopy with simultaneous neurophysiological recordings in hippocampal brain slices. Either of two Ca2+-sensitive dyes were injected into CA1 pyramidal neurons. Direct depolarization of the neurons via the somatic electrode produced clear increases in Ca2+ signals within the dendritic spines, a result that was not predicted by the previous spine model. Our new spine model suggests that some of this signal could theoretically result from Ca2+-bound dye diffusing from the dendritic shaft into the spine. Dye diffusion alone cannot, however, explain the numerous cases in which the Ca2+ signal in the spine was considerably larger than that in the adjacent dendritic shaft. The latter observations raise the possiblity of voltage-gated Ca2+ entry directly into the spine or else perhaps via Ca2+-dependent Ca2+release. The new spine model accommodates these observations as well as several other recent experimental results. 1994 John Wiley & Sons, Inc.  相似文献   
8.
Wagner  U.  Reinsberg  J.  Schmidt  S.  Mallmann  P.  Schmolling  J.  Schultes  B.  Richter  H.  Biersack  H. J.  Krebs  D. 《Cell biochemistry and biophysics》1994,24(1-3):237-242
Antibodies can be processed by the B- and T-cell systems and may lead to a selective activation of the immune system. The network structure of the immune system implicates the possibility of a selective immunization by the activation of idiotypic cascades. In a retrospective analysis, patients with advanced ovarian carcinoma, who had received MAb, against the cancer-associated antigen CA125 for diagnostic purposes, were analyzed for the production of anti-idiotypic antibodies, survival rate, and immunological effects. Furthermore, we started a prospective and randomized study for ovarian cancer patients, using a different antigen, TAG72, for the induction of idiotypic cascades. Our first results on 58 patients with advanced ovarian carcinomas showed that the induction of anti-idiotypic-antibodies against OC125 mimicking the TAA Class III CA125 leads to a prolongation of the survival rate, and, in extended stages, to an induction of antitumoral immunity, and that the induction of idiotypic cascades is also possible for different antigens like TAG72. Summarizing the activation of idio-typic network cascades seems to be a very effective way of intervention in the immune system of patients with advanced stages of ovarian carcinoma. A prospective study of the adjuvant approach seems to be necessary.  相似文献   
9.
摘要 目的:探讨经阴道三维超声联合糖类抗原125(CA125)、糖类抗原199(CA199)、中性粒细胞/淋巴细胞比值(NLR)及血小板/淋巴细胞比值(PLR)检测对绝经后女性子宫内膜癌(EC)的诊断效能。方法:回顾性分析本院2019年5月至2022年5月收治的因绝经后出血就诊的92例疑似子宫内膜肿瘤患者的病历资料,经手术病理证实,EC患者48例(EC组)、子宫内膜良性病变患者44例(良性组)。比较两组CA125、CA199、NLR及PLR水平,对比两组子宫内膜血管指数(VI)、血流指数(FI)、血管-血流指数(VFI)、子宫内膜容积(EV)变化及血流信号分布情况。绘制受试者工作特征(ROC)曲线分析经阴道三维超声联合CA125、CA199、NLR及PLR检测对绝经后EC的诊断效能。结果:EC组CA125、CA199、NLR及PLR水平均高于良性组(P<0.05)。EC组三维超声参数VI、FI、VFI及EV均高于良性组(P<0.05)。EC组血流信号Ⅱ级占比25.00%,Ⅲ级占比70.83%;良性组血流信号Ⅱ级占比88.64%,Ⅲ级占比2.27%。EC组血流信号Ⅱ级占比低于良性组,血流信号Ⅲ级占比高于良性组(P<0.05)。两组血流信号0级、Ⅰ级比较无差异(P>0.05)。ROC结果显示五项检查联合检测曲线下面积(AUC)值为0.944(95%Cl:0.902~0.985),具有更优的诊断效能(敏感度为89.10%、特异度为91.80%)。结论:CA125、CA199、NLR及PLR检测联合经阴道三维超声检查诊断绝经后EC效果显著,可为临床诊断提供参考。  相似文献   
10.
The mdr1 gene, first member of the human multidrug-resistance gene family, is a major gene involved in cellular resistance to several drugs used in anticancer chemotherapy. Its product, the drug-excreting P-glycoprotein, shows a bipartite structure formed by two similar adjacent halves. According to one hypothesis, the fusion of two related ancestral genes during evolution could have resulted in this structure. The DNA sequence analysis of the introns located in the region connecting the two halves of the human mdr1 gene revealed a highly conserved poly(CA) · poly (TG) sequence in intron 15 and repeated sequences of the Alu family in introns 14 and 17. These repeated sequences most likely represent molecular fossils of ancient DNA elements which were involved in such a recombination event. Correspondence to: M. Pauly  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