全文获取类型
收费全文 | 9385篇 |
免费 | 723篇 |
国内免费 | 443篇 |
专业分类
10551篇 |
出版年
2024年 | 22篇 |
2023年 | 79篇 |
2022年 | 237篇 |
2021年 | 393篇 |
2020年 | 273篇 |
2019年 | 282篇 |
2018年 | 316篇 |
2017年 | 259篇 |
2016年 | 378篇 |
2015年 | 562篇 |
2014年 | 615篇 |
2013年 | 712篇 |
2012年 | 803篇 |
2011年 | 746篇 |
2010年 | 475篇 |
2009年 | 347篇 |
2008年 | 482篇 |
2007年 | 398篇 |
2006年 | 383篇 |
2005年 | 316篇 |
2004年 | 274篇 |
2003年 | 231篇 |
2002年 | 227篇 |
2001年 | 173篇 |
2000年 | 189篇 |
1999年 | 138篇 |
1998年 | 85篇 |
1997年 | 82篇 |
1996年 | 77篇 |
1995年 | 59篇 |
1994年 | 63篇 |
1993年 | 48篇 |
1992年 | 90篇 |
1991年 | 76篇 |
1990年 | 77篇 |
1989年 | 61篇 |
1988年 | 47篇 |
1987年 | 67篇 |
1986年 | 45篇 |
1985年 | 37篇 |
1984年 | 33篇 |
1983年 | 20篇 |
1982年 | 25篇 |
1980年 | 22篇 |
1979年 | 26篇 |
1978年 | 19篇 |
1977年 | 21篇 |
1975年 | 18篇 |
1973年 | 21篇 |
1972年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
Uptake of d-glucosamine by rat brain synaptosomes occurs via a saturable transport process (Km 2.1 mM, V 3.0 nmol/mg per min) which was clearly distinguishable from simple diffusion. This transport process is highly sensitive to cytochalasin (Ki = 7 · 10?5 mM. d-Glucose competitively inhibits d-glucosamine uptake with a Ki value of 8 · 10?1 mM. 相似文献
62.
The effect of 2-bromopalmitate, an inhibitor of fatty acid oxidation, on progesterone synthesis in isolated luteal cells was studied. Incubation of the cells with increasing concentrations (0 – 2 mM) of the inhibitor resulted in an initial enhancement of progesterone synthesis, both in the presence and absence of LH (1 μg/m1). In the LH-treated cells, this stimulation in steroid synthesis becomes markedly impaired at 2 mM 2-bromopalmitate. In the control cells, however, progesterone synthesis was sustained at the elevated level. At high concentrations of 2-bromopalmitate, the stimulatory effect of LH (relative to the controls) on steroidogenesis was progressively diminished, until it was completely abolished at an inhibitor concentration of 2 mM. The oxidation of labelled palmitic acid by luteal cells was also effectively inhibited by 2-bromopalmitate (1 mM). The results indicate that the steroidogenic effect of LH is mediated, in part, by fatty acid oxidation, and were explained in terms of the interaction between carbohydrate and fatty acid oxidation in supporting ovarian steroidogenesis. 相似文献
63.
When flax seedlings are decapitated above cotyledons and three days later one of the two cotyledons is removed then the remaining
cotyledon stimulates in four to five days growth of its axillary bud. It has been found that content of endogenous cytokinins
was higher in the stimulated bud as compared with the other one already 12 h after the cotyledon removal.
Flax seedlings decapitated under cotyledons regenerate adventitious buds on thy hypocotyl stump during 5–6 days. The endogenous
fytohormonal preparation of this regeneration was investigated in the 20 mm apical part of the hypocotyl stump. Decrease in
auxin and increase in gibberellins was already found during the first day after decapitation while the level of cytokinins
increased as late as three days after the apex removal. 相似文献
64.
[3H]Mepyramine binds with high affinity to membranes from brain of human, rat, guinea-pig, rabbit and mouse with drug specificity indicating an association with histamine H1receptors. Considerable species differences occur in the affinity of [3H]mepyramine, with guinea-pig and human having 34 times greater affinity than rat, mouse or rabbit. The greater affinity of [3H]mepyramine in guinea-pig than in rat is attributable both to faster association and slower dissociation rates in guinea-pig. Species differences in affinity for H1 receptor sites occur for some antihistamines but not for others. Some tricyclic antidepressant and neuroleptic drugs are extremely potent inhibitors of [3H]mepyramine binding, exceeding in potency any H1 antihistamines examined. The tricyclic antidepressant doxepin and the neuroleptic clozapine are the most potent of all drugs examined in competing for [3H]mepyramine binding. The regional distribution of specific [3H]mepyramine binding differs considerably in the various species examined. 相似文献
65.
Nineteen patients who had completed their course of dermatattoo treatment for the camouflage of port-wine hemangioma were evaluated at an average of 3.1 years following completion of treatment. A panel of 7 people evaluated preoperative and postoperative photographs and judged that none of the patients were more than "50 percent improved" in the camouflaging of their hemangioma, and that most of them (15 out of 19) were either "not improved" or "25 percent improved," as compared to their original photographs. We cannot rule out the possibility that this treatment may be effective in adults, as all of our patients at the time of their first treatment were between the ages of 4 and 20 years; and most of them were between 6 and 10 years old. On the basis of this evaluation, we no longer recommend the technique of dermatattoo for camouflage of port-wine hemangioma in patients in the younger age group. 相似文献
66.
Lasse Ryhänen Elaine M.L. Tan Sirpa Rantala-Ryhänen Jouni Uitto 《Archives of biochemistry and biophysics》1982,215(1):230-236
Chick embryo sterna, which actively synthesize type II procollagen, were pulse-labeled with radioactive proline; protein synthesis was then inhibited by unlabeled proline and cycloheximide. After the inhibition of protein synthesis, several amino acids, polyamines, or structurally related compounds were added to the incubation medium. The conversion of procollagen, first to two intermediates, pC-collagen and pN-collagen, and then to collagen, was monitored by sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis. The addition of 50 mm β-alanine, arginine, asparagine, glutamine, hydroxylysine, lysine, or ornithine, as well as agmatine, ?-aminocaproic acid, S-2-aminoethylcysteine, cadaverine, canavanine, putrescine, or spermine clearly inhibited the removal of the carboxy-terminal extension and pC-collagen accumulated; the removal of the amino-terminal extension was not affected. The inhibition of the conversion was reversible and unaffected by fetal calf serum. The results suggest that the conversion of type II procollagen to collagen requires at least two separate proteinases for the removal of amino-terminal and carboxy-terminal extensions. The results further suggest that naturally occurring molecules may be used to modulate the rate of conversion of procollagen to collagen, and development of analogs of these compounds may provide the means to interfere with excessive deposition of collagen in diseases with tissue fibrosis. 相似文献
67.
The chemical identity of the immunoreactive LHRH-like peptide biosynthesized in the human placenta 总被引:5,自引:0,他引:5
Freshly obtained human placental trophoblasts were minced and pulselabeled for 30 min at 37°C with tritiated L-Tyrosine. After homogenisation, the crude extract was centrifuged and deproteinized with 10% TCA. The supernatant was defatted and the peptides concentrated through hydrophobic binding on ODS-silica cartridges. The bound, crude peptide extract was eluted and subjected to gradient, reverse-phase High Performance Liquid Chromatography. The fractions corresponding to the absorption peak of reference, synthetic LHRH were collected and extensively purified to radioactive homogeneity by further multiple HPLC. After digestion with pyroglutamate aminopeptidase, the resulting nonapeptide was manually sequenced by dansyl-Edman degradation. All the incorporated radioactivity was found to reside exclusively in residue number 4 of the nonapeptide; thus establishing for the first time the primary sequence of biosynthetic placental LHRH as: pGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH2, identical to its hypothalamic counterpart. 相似文献
68.
A C Tan W H Hoefnagels A A Gerritsen R W Jansen P W Kloppenborg T J Benraad 《Hormones et métabolisme》1991,23(9):435-437
The influence of mild dehydration on plasma levels of atrial natriuretic peptide (ANP) was studied in both young (aged 18 to 25 years) and elderly (aged 72 to 86 years) subjects. We expected that dehydration would lower ANP concentrations due to the ensuing volume contraction. A different response of the ANP hormonal system in the elderly might help to explain the observation that elderly subjects are more predisposed to dehydration as compared to young subjects. Dehydration was induced by restriction of fluid intake to 25% of normal for one day. During the study, urinary osmolality increased while osmolar clearance and body weight decreased. Basal ANP concentrations were higher in the elderly subjects. However, these levels did not change during the dehydration study neither in the young nor in the elderly subjects. This may be explained by the activation of counter-regulatory systems preventing a decrease in central blood volume and hence a decrease in ANP concentration. 相似文献
69.
本文报道用自旋非限制Hartree-Fock方法(spin unrestricted Hartree-Fock method简写UHF)对氧合血红蛋白的Fe-O2键合态进行ab initio研究。结果表明Fe(Ⅱ)、Oc和Or的Mulliken布居值分别为24.18、8.19和7.64。这说明氧合血红蛋白的Fe-O2键合态不发生电子转移。研究模型所得到的频率与实验频率基本一致。研究结果不支持Weiss提出的Fe3+O2-模型,为解释血红蛋白传输氧的作用机理提供了新的理论依据。 相似文献
70.
1985年我们采用间接免疫荧光法(IF法)检测出甲肝患者外周血白细胞中有甲肝抗原(HAAg)存在,继而又将HAAg阳性白细胞直接种入PLC/PRF/5细胞,分离到两株甲肝病毒(HAV)NJ—3株和H—1株。为了弄清白细胞所携带的病毒究竟仅为吸附吞饮,抑或能在其中复制增殖,我们将分离到的HAV用正常人血白细胞进行体外增殖试验,现将结果报告如下。 相似文献