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   1478篇
  免费   78篇
  国内免费   1篇
  2022年   6篇
  2021年   14篇
  2019年   11篇
  2018年   17篇
  2017年   13篇
  2016年   25篇
  2015年   41篇
  2014年   32篇
  2013年   102篇
  2012年   75篇
  2011年   92篇
  2010年   54篇
  2009年   48篇
  2008年   88篇
  2007年   81篇
  2006年   71篇
  2005年   66篇
  2004年   65篇
  2003年   53篇
  2002年   61篇
  2001年   54篇
  2000年   59篇
  1999年   40篇
  1998年   19篇
  1997年   17篇
  1996年   7篇
  1995年   12篇
  1994年   11篇
  1993年   13篇
  1992年   33篇
  1991年   23篇
  1990年   17篇
  1989年   18篇
  1988年   19篇
  1987年   16篇
  1986年   14篇
  1985年   12篇
  1984年   25篇
  1983年   19篇
  1982年   7篇
  1981年   8篇
  1980年   8篇
  1979年   12篇
  1978年   7篇
  1975年   9篇
  1973年   8篇
  1970年   5篇
  1969年   5篇
  1968年   5篇
  1967年   7篇
排序方式: 共有1557条查询结果,搜索用时 15 毫秒
1.
BACKGROUND: We report a successful pregnancy in a woman with severe ovarian dysfunction and infertility associated with a variant beta-subunit of luteinizing hormone (LH). METHOD/OUTCOME: A 35-year-old woman consulted our unit for infertility. Laparoscopy and ultrasonography showed obstruction of the right tube and ovulation from the right ovary only. Human menopausal gonadotrophin (hMG) therapy was used for six subsequent cycles, but did not result in conception. Subsequently, marked elevation of follicle-stimulating hormone (FSH) and testosterone, together with polycystic ovary (PCO) were noted. The patient failed to respond to ovarian stimulation by hMG. Severe ovarian dysfunction such as premature ovarian failure (POF) was strongly suspected. Sequence analysis of the LH beta-subunit gene indicated heterozygosity for point mutations Trp(8) to Arg(8) and Ile(15) to Thr(15) in the coding sequence. LH hypersecretion resembling that seen in PCO syndrome was observed. Induction of ovulation by hMG was successful in the first cycle in which the basal LH and FSH were well controlled with gonadotrophin-releasing hormone analog following estrogen-progesterone replacement. She conceived and delivered a healthy male infant at term. CONCLUSION: Clinicians should be clinically aware of patients with immunologically anomalous LH variant who might be at risk of developing ovarian failure within a relatively short time span. Pertinent treatment should be applied without delay in such cases.  相似文献   
2.
The binding and internalization of 125I-nerve growth factor (NGF) by PC12 pheochromocytoma cells was studied as a function of extracellular potassium concentration. Both surface-bound and internalized fractions of 125I-NGF associated with the cells under depolarizing conditions (50 mM K+) increased to 144 +/- 28% (average +/- SEM, six different cell preparations) and to 176 +/- 12% (n = 6), respectively, of those observed at 6.0 mM K+. Scatchard-type analysis of the data indicates increased sites for the binding and internalization of iodinated NGF by the cells. Similar enhancement was observed for cells treated with NGF as well. This voltage-dependent phenomenon was reversible, and also observed in the presence of veratridine. Moreover, withdrawal of extracellular Ca2+ abolished high K+-induced modulation of 125I-NGF binding and internalization, indicating that this effect may be mediated by Ca2+.  相似文献   
3.
Summary The antitumor effect of recombinant human tumor necrosis factor (rH-TNF) on two clones of rat fibrosarcoma with different metastatic potential to lymph nodes was examined. The colony formation of clone A, which has high metastatic potential, was completely inhibited by continuous exposure to rH-TNF at 50 U/ml. In contrast, colony formation of clone G, which has low metastatic potential, was not inhibited by high concentrations of rH-TNF (10,000 U/ml). The inhibitory effect of rH-TNF on colony formation by clone A was also observed with a 1-h exposure to rH-TNF. This effect was time and concentration dependent, as determined by the colony assay, 3H-thymidine uptake assay, and 51Cr-release assay. 3H-thymidine and 3H-uridine uptake per cell of clone A exposed to rH-TNF was not decreased. This suggests that the mechanisms of the antitumor effect of rH-TNF were not due to inhibition of DNA and RNA synthesis of tumor cells. In vivo growth and lymph node metastases of clone A inoculated i.p. to Donryu strain rats were completely suppressed by 14 consecutive i.p. injections of 105 or 106 U/kg per day of rH-TNF. On the other hand the growth of clone G was not influenced by rH-TNF administration.  相似文献   
4.
Summary We investigated possible association of and linkage between HLA and familial polyposis coli (FPC). In 182 individuals from 66 pedigrees of FPC and 108 individuals from a normal population, HLA-A,-B, and-C antigens were determined. When the frequencies of HLA antigens in 66 unrelated patients and in normal controls were compared, no association of FPC with HLA was observed. For the linkage analysis, HLA haplotypes of 17 affected sib pairs were investigated by the affected sib pair method. The number of pairs which shared two, one, and no haplotypes identical by descent was not significantly different from the number expected with random occurrence (P>0.95). Finally, seven families were analyzed using Morton's sequential test. A maximum lod score of-0.056 at a recombination fraction of 0.4, and a lod of-3.089 at a recombination fraction of 0.05 were obtained. Therefore, there is neither an association of nor linkage between FPC and HLA.  相似文献   
5.
This study indicates that acupuncture and moxibustion stimulation on one side can inhibit Exteroceptive vibration-induced finger flexion reflex (VFR) produced by vibration on the surface of the skin of fingers of both hands. This was thought to be due to that transmission of impulses in the spinal cord producing VFR was inhibited bilaterally, when unilateral acupuncture or moxibustion stimulus was applied. The degree of inhibition with acupuncture and moxibustion stimulation was, in decreasing order, electroacupuncture (insulated needle), electroacupuncture (stainless needle), leaving needle, indirect moxibustion and cold moxibustion in the ipsilateral side, and the order of the leaving needle and the indirect moxibustion was reversed in the contralateral side. By investigating the effects of stimulation of meridian points and their neighboring places, the location of stimulation where VFR was effectively inhibited was found. Furthermore, the role played by the organization metamerism was demonstrated. Also prostaglandin was considered to mediate the effects of acupuncture stimulation on VFR. Concurrent stimulation of the Hég? (LI4) and B?ihuì (GV 20) did not inhibit VFR. In many of the subjects with no manifestation of VFR, VFR occurred when acupuncture stimulus was applied to the B?ihuì.  相似文献   
6.
During postnatal development, UDP-Gal: GlcNAc(beta 1-4)-galactosyltransferase (4 beta-GT) and UDP-Gal:GalNAc(beta 1-3)-galactosyltransferase (3 beta-GT) activities were increased by 17- and 24-fold, respectively, in the rat small intestine. The injection of cortisone into suckling rats resulted in precocious induction of distal 4 beta- and 3 beta-GT activities by 2.7- and 1.8-fold, respectively. Injection of phorbol-12-myristate-13-acetate (PMA) resulted in precocious induction of distal 3 beta-GT by 2.7-fold. These results suggest that intestinal galactosyltransferase activities are under developmental regulation and can be modified by cortisone and PMA.  相似文献   
7.
Calyculin A and okadaic acid: inhibitors of protein phosphatase activity   总被引:44,自引:0,他引:44  
Calyculin A and okadaic acid induce contraction in smooth muscle fibers. Okadaic acid is an inhibitor of phosphatase activity and the aims of this study were to determine if calyculin A also inhibits phosphatase and to screen effects of both compounds on various phosphatases. Neither compound inhibited acid or alkaline phosphatases, nor the phosphotyrosine protein phosphatase. Both compounds were potent inhibitors of the catalytic subunit of type-2A phosphatase, with IC50 values of 0.5 to 1 nM. With the catalytic subunit of protein phosphatase type-1, calyculin A was a more effective inhibitor than okadaic acid, IC50 values for calyculin A were about 2 nM and for okadaic acid between 60 and 500 nM. The endogenous phosphatase of smooth muscle myosin B was inhibited by both compounds with IC50 values of 0.3 to 0.7 nM and 15 to 70 nM, for calyculin A and okadaic acid, respectively. The partially purified catalytic subunit from myosin B had IC50 values of 0.7 and 200 nM for calyculin A and okadaic acid, respectively. The pattern of inhibition for the phosphatase in myosin B therefore is similar to that of the type-1 enzyme.  相似文献   
8.
Summary l-Threonine hyper-producing mutants were obtained fromEscherichia coli W strain KY-8366, by reducingl-threonine degradation activity and enhancingl-threonine biosynthetic activity. Anl-threonine degradation reaction test using resting cells of KY-8366 suggested that the main pathway ofl-threonine degradation by KY-8366 is via glycine. A strain with reducedl-threonine degradation activity was obtained among those mutants that could not utilizel-threonine as sole nitrogen source. Rifampicin-resistant mutants andl-lysine plus methionine-insentitive mutants were isolated. These mutants showed enhanced aspartokinase levels and accumulated morel-threonine than the parental strains. Mutant H-4290 accumulated 58 g/l ofl-threonine.  相似文献   
9.
The possibility that plant growth regulators may relate to a cyclic 3:5 adenosine monophosphate (cAMP)-dependent protein kinase through the control of cAMP level in the conidial germination process of Neurospora crassa was examined using a cAPM-dependent protein kinase mutant (cpk mutant) which is thought to be cAMP-independent because of defect in the regulatory subunit of cAMP-dependent protein kinase. IAA, 2,4-D and GA3 promoted conidial germination and elongation of young hyphae in the mutant as well as in the wild-type. The result suggests that the effects of auxin and gibberellin on germination and hyphal elongation are not mediated by cAMP.  相似文献   
10.
Summary Growth and l-threonine productivity of l-threonine producer Escherichia coli H-4290 were inhibited by precursor amino acids, l-homoserine and l-aspartate. l-Threonine hyper-producers were isolated among the mutants resistant to l-homoserine and l-aspartate. Mutants H-4351 (Homr) and H-4578 (Homr, Aspr) accumulated 22.2 g/l and 24.3 g/l of l-threonine in test tube cultures, while the parental strain H-4290 accumulated 18.2 g/l. The enzyme level of aspartokinase I (first enzyme of the threonine operon) was enhanced 2.3 times (H-4351) and 3 times (H-4578) that of H-4290. Mutant H-4578 accumulated 76 g/l of l-threonine in a 2-l jar fermentor after 75 h cultivation.Abbreviations DAP diaminopimeric acid - Met l poor growth in methionine-free medium - AHV -amino--hydroxyvaleric acid - Thr-N- lack of ability to utilize l-threonine as a nitrogen source - Rif rifampicin - Lys+Metr resistant to l-lysine and dl-methionine  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