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   3285篇
  免费   199篇
  2023年   5篇
  2022年   16篇
  2021年   34篇
  2020年   20篇
  2019年   37篇
  2018年   52篇
  2017年   55篇
  2016年   79篇
  2015年   112篇
  2014年   144篇
  2013年   181篇
  2012年   220篇
  2011年   217篇
  2010年   155篇
  2009年   160篇
  2008年   251篇
  2007年   222篇
  2006年   231篇
  2005年   224篇
  2004年   231篇
  2003年   169篇
  2002年   204篇
  2001年   32篇
  2000年   32篇
  1999年   35篇
  1998年   37篇
  1997年   29篇
  1996年   34篇
  1995年   19篇
  1994年   25篇
  1993年   19篇
  1992年   17篇
  1991年   18篇
  1990年   21篇
  1989年   15篇
  1988年   9篇
  1987年   12篇
  1986年   12篇
  1985年   16篇
  1984年   16篇
  1983年   17篇
  1982年   8篇
  1981年   4篇
  1980年   3篇
  1979年   7篇
  1978年   3篇
  1977年   4篇
  1975年   4篇
  1974年   3篇
  1970年   3篇
排序方式: 共有3484条查询结果,搜索用时 296 毫秒
1.
Serum total thyroxine (T4), total triiodothyronine (T3), T4-binding globulin (TBG), free T4(FT4) and free T3(FT3) concentrations and the T3-uptake(T3-U) value were estimated in 11 patients with subacute thyroiditis, and compared with the same parameters in 11 patients with Graves' disease, whose serum T4 concentrations were similar to the former group. Seven patients with subacute thyroiditis, who were treated with dicrofenac sodium alone, were investigated as to the sequential changes in serum parameters during their clinical courses. The mean serum T3-U value and FT4, T3 and FT3 concentrations in patients with subacute thyroiditis were increased, but all were significantly lower than those in patients with Graves' disease (p less than 0.01, p less than 0.001, p less than 0.001 and p less than 0.001, respectively). Three patients with subacute thyroiditis, who showed shorter duration of symptoms than 10 days, had serum TBG excess. Thus the mean (+/- SD) serum TBG concentration (26.5 +/- 8.4 micrograms/ml) was significantly higher than that (18.3 +/- 2.9 micrograms/ml) in patients with Graves' disease (p less than 0.02). The ratios of serum T3 to T4 and FT3 to FT4 in patients with subacute thyroiditis were also significantly lower than those in patients with Graves' disease (p less than 0.001 and p less than 0.001, respectively). The serum FT4 in 7 patients treated with dicrofenac sodium alone decreased to the normal range after 3 to 8 weeks from the onset of the illness. In 3 patients with TBG excess and one patient (TBG; 29.0 micrograms/ml), serum TBG declined in consequence of the serum FT4 normalization.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
2.
A synthetic 17 amino acid peptide (CKS-17) homologous to a highly conserved region of human and animal retroviral transmembrane proteins was investigated for its influence on the in vitro production of IFN-gamma from human peripheral mononuclear cells. The results showed that CKS-17 coupled to a carrier protein, BSA, inhibited production of IFN-gamma in a dose-dependent manner. Controls, consisting of BSA, which had undergone the coupling procedure or neurotensin coupled to BSA in an identical manner as CKS-17, showed no such inhibition. Reduction in IFN-gamma production could not be attributed to decreased viability of cells, delay of IFN-gamma production or to involvement of suppressor cells. Moreover, inhibition of IFN-gamma production was not related to the inhibition of DNA synthesis. The inhibition appeared to be a direct effect of CKS-17 on IFN-gamma-producing cells. Kinetic studies revealed that this suppression occurred when CKS-17 was introduced to the culture concurrent with or within 48 h after introduction of IFN inducers. Preincubation experiments showed that the presence of CKS-17 in the culture medium was not necessary to exert its inhibitory effect. These results suggest that a portion of retroviral envelope proteins possess important immunomodulatory actions.  相似文献   
3.
Rotational diffusion of the total cytochrome P-450 (P-450scc plus P-45011 beta) in bovine adrenocortical mitochondria was examined by observing the decay of absorption anisotropy, r(t), after photolysis of the hemo.CO complex by a vertically polarized laser flash. Analysis of r(t) was based on a "rotation-about-membrane normal" model. The measurements were used to investigate intermolecular interactions of cytochrome P-450 with other membrane proteins. The absorption anisotropy decayed within 1 ms to a time-independent value. Rotational diffusion of cytochrome P-450 was dependent on the presence and absence of deoxycorticosterone (DOC), a substrate for cytochrome P-45011 beta. The observed value for the normalized time-independent anisotropy r(infinity)/r(0) and the average rotational relaxation time phi are r(infinity)/r(0) = 0.88 and phi = 233 microseconds when DOC is absent, and r(infinity)/r(0) = 0.65 and phi = 350 microseconds when DOC is present. Judging from the phi value, rotating P-450 is not a monomeric molecule, but would be a small microaggregate with an average diameter of about 120 A. A significantly high value of r(infinity)/r(0) implies co-existence immobile populations of cytochrome P-450. Based on the assumption that the heme angle tilts 55 degrees from the membrane plane (Gut et al. (1983) J. Biol. Chem. 258, 8588-8594), 65% (when DOC is present) or 88% (when DOC is absent) of cytochrome P-450 in mitochondria is immobilized within the experimental time range of 2 ms due to the presence of immobile protein microaggregates.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
4.
H Aiba  T Nakamura  H Mitani    H Mori 《The EMBO journal》1985,4(12):3329-3332
Mutations which permit cAMP binding protein (CRP) to act in the absence of cAMP have been isolated by in vitro mutagenesis of a plasmid containing the cloned crp gene. Adenylate cyclase deficient cells harbouring the mutant (crp*) plasmids exhibited a variety of fermentation profiles on MacConkey indicator plates containing various sugars. beta-galactosidase synthesis in cells carrying the crp* plasmids was activated most by the addition of cGMP as well as cAMP. The sites of mutations which are responsible for the cAMP independent phenotype were determined by in vitro recombination and DNA sequencing. The amino acid substitutions in the mutant proteins were found in two specific regions of the crp gene encoding residues 53-62 and 141-148 of CRP polypeptide. The first region may participate in cAMP binding, while the second appears to be the inter-domain region of the N-terminal cAMP-binding and C-terminal DNA-binding domains.  相似文献   
5.
Japanese monkeys often exchange the particular vocal sound, “coo,” especially when they feed or move as a group. It was considered that the “coo” sound had no positive social meaning, perhaps because the “coo” sound network and its function were hidden behind other behavioral observations. For identification of the vocalizer only from hearing the “coo” sound, three phonetic values, i.e., the “fundamental,” “duration,” and “formants,” plus other characteristics were used as indices of voiceprints. The results indicated that these were effective for identifying the vocalizer in two-thirds of the adults in the study troop which was composed of 12 adults and 16 immature members. The “coo” sound exchange network among the troop members (adults) was drawn on the basis of the voiceprint identification. The network showed three characteristics as follows: (1) matriarchs of the kin-groups frequently exchanged “coo” sounds with each other; (2) the other females exchanged “coo” sounds mostly within their own kin-groups; and (3) males seldom participated in the “coo” sound exchange. This suggests that “coo” sound exchange plays a central role for the matriarch of kin-groups in binding each kin-group and, ultimately, in binding all members together into an organized troop.  相似文献   
6.
To study the gene products of the HLA complex, we produced two monoclonal antibodies, termed HU-18 and HU-23. They were active in complement-dependent cytotoxicity and detected B-cell alloantigens encoded by a locus (or loci) linked to HLA. When three types of HLA-DR4 homozygous B-cell lines with different HLA-D specificities were tested for reactivity with HU-18 and HU-23, they displayed distinct reaction patterns depending on the HLA-D specificities they possessed: EBV-Wa (HLA-DYT homozygous), negative for both HU-18 and HU-23; KT2 and KOB (HLA-DKT2 homozygous), positive only for HU-18; and ER (HLA-Dw4 homozygous), positive for both. These differential reaction patterns were further confirmed by testing against a panel of 17 HLA-DR4-positive peripheral blood lymphocytes with known HLA-D specificities. Thus, these monoclonal antibodies allow us to identify HLA-DYT, HLA-DKT2, and HLA-Dw4 solely by serologic methods. This is the first clearcut serologic identification of these three HLA-DR4-associated HLA-D specificities, which have been indistinguishable by conventional serology and identified only by cellular techniques. It is hoped that immunochemical investigations using HU-18 and HU-23 will advance our understanding of the HLA-D region on a molecular level.  相似文献   
7.
8.
Mitani, Michiko (National Institute of Genetics, Mishima, Japan), and Tetsuo Iino. Electron microscopy of bundled flagella of the curly mutant of Salmonella abortivoequina. J. Bacteriol. 90:1096-1101. 1965.-The arrangement of flagella was observed by dark-field and electron microscopy in three strains of Salmonella abortivoequina, namely, normal flagellar, curly flagellar, and paralyzed curly flagellar strains. With dark-field microscopy, bundled flagella could be seen in 5 to 10% of actively moving normal or curly mutant cells. Under the electron microscope, a great many bundled flagella were observed in the curly mutant strain, but in the normal strain most of the flagella were dissociated or the bundles were rather loose and irregular. Normal flagella seem to separate easily during the process of preparation, but not the curly ones. Single flagella were found to run parallel with each other and to form a bundle consisting of five or more flagella; the bundle was spirally gyrating, with the characteristic flagellar wave. It is thought that the bundle observed with the electron microscope corresponds to that observed under the dark-field microscope. Further, the marked decrease of bundle formation in the paralyzed curly mutant cells suggests that bundle formation is not caused by curly flagellar structure per se, but corresponds to the mode of locomotion of peritrichously flagellated bacteria.  相似文献   
9.
Monocytes (MO) influenced phosphoinositide metabolism when human T lymphocytes, isolated from peripheral blood, were activated by polyclonal mitogens. In the 3 hr immediately following mitogenic challenge, the synthesis of phosphatidylinositol (PI) was augmented and the synthesis of PI-4-phosphate (PIP) and PI-4,5-bisphosphate (PIP2) was induced in cultures of T lymphocytes and MO. In addition, MO induced a rapid and transient degradation of PIP and PIP2 in T cells prelabeled with [32P]PL and subsequently activated by mitogen. Induction of a PIP/PIP2 response correlated well with induction of DNA replication by MO when T cells were activated by phytohemagglutinin or by neuraminidase plus galactose oxidase. MO did not influence polyphosphoinositide metabolism when T cells were stimulated by the nonmitogenic lectin wheat germ agglutinin. Interleukin 1 could not substitute for monocytes in inducing a polyphosphoinositide response. By causing a rapid and transient release of the second messengers diacylglycerol and inositol phosphates and by subsequently increasing their cellular precursors, MO may induce the interleukin 2 responsive state in T lymphocytes.  相似文献   
10.
A quantitative analysis of glutamate in brain dialysate was made by using an enzymatic cycling technique. This method made it possible to measure the concentration of glutamate in dialysate collected at 30-s intervals. Dialysates were collected from Mongolian gerbil hippocampus before, during, and after two 90-s ischemic insults at an interval of 5 min. An extracellular increase in levels of glutamate was already observed in samples collected during a 30-60 s period after the onset of each ischemia, and the levels of glutamate were maximal at the end of each period of ischemia (approximately a fourfold increase). The increased levels of glutamate rapidly returned almost to preischemic levels by 30 s of recirculation. This method will provide more precise information about temporal changes in the extracellular glutamate concentration in the brain during ischemia.  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