全文获取类型
收费全文 | 23487篇 |
免费 | 2208篇 |
国内免费 | 12篇 |
专业分类
25707篇 |
出版年
2023年 | 110篇 |
2022年 | 224篇 |
2021年 | 446篇 |
2020年 | 257篇 |
2019年 | 323篇 |
2018年 | 405篇 |
2017年 | 354篇 |
2016年 | 575篇 |
2015年 | 939篇 |
2014年 | 1046篇 |
2013年 | 1261篇 |
2012年 | 1678篇 |
2011年 | 1501篇 |
2010年 | 1019篇 |
2009年 | 975篇 |
2008年 | 1292篇 |
2007年 | 1310篇 |
2006年 | 1195篇 |
2005年 | 1212篇 |
2004年 | 1114篇 |
2003年 | 1038篇 |
2002年 | 1011篇 |
2001年 | 347篇 |
2000年 | 323篇 |
1999年 | 352篇 |
1998年 | 319篇 |
1997年 | 270篇 |
1996年 | 243篇 |
1995年 | 196篇 |
1994年 | 210篇 |
1993年 | 207篇 |
1992年 | 221篇 |
1991年 | 197篇 |
1990年 | 263篇 |
1989年 | 221篇 |
1988年 | 188篇 |
1987年 | 202篇 |
1986年 | 146篇 |
1985年 | 204篇 |
1984年 | 181篇 |
1983年 | 131篇 |
1982年 | 159篇 |
1981年 | 136篇 |
1980年 | 125篇 |
1979年 | 131篇 |
1978年 | 109篇 |
1977年 | 98篇 |
1976年 | 106篇 |
1974年 | 101篇 |
1973年 | 91篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
22.
Frank Josef Mller Oliver Zierau Torsten Hertrampf Anja Bliedtner Patrick Diel Günter Vollmer 《The Journal of steroid biochemistry and molecular biology》2009,113(3-5):296-303
Isoflavones (ISOs) are bioactive food ingredients of the traditional East Asian diet and currently discussed as alternatives to classical hormone replacement therapies and for reducing the prevalence of hormone-dependent cancers. Although there are many studies on ISOs, not much is known about their long-term effects.Therefore, we performed an animal experiment analyzing the effects of three different diets: a phytoestrogen-free diet, a diet supplemented with genistein (700 μg/g diet) and an ISO-high diet (232 μg daidzein and 240 μg genistein/g) at two distinct time points, juvenile (21 days) and adult (97 days). Exposure started prior to mating of the parents and throughout the life of the offspring.We observed a stronger increase of uterine wet weights in juvenile offspring with genistein exposure (1018 ± 350 mg/kg BW) than with ISO-high diet (497 ± 133 mg/kg BW). Whereas the expression of proliferation related genes (PCNA; Ki67; IGF-1; IGF-1R), analyzed by real-time-qPCR and Western blot, were significantly down-regulated in juvenile animals exposed to genistein. Additionally, genistein exposure led to estrogenic responses, observed upon increase of complement C3 and decrease of estrogen receptors gene expressions, while the exposure to ISO-high diet did not show these effects.In conclusion, both the time point on which phytoestrogen exposure starts together with the composition of the ingested phytoestrogen containing diet are of great importance for the biological response of the offspring. 相似文献
23.
24.
J.F. Kuo Eugene J. Malveaux Janice G. Patrick Craig W. Davis Albert W. Pruitt 《Biochimica et Biophysica Acta (BBA)/General Subjects》1977,497(3):785-796
Possible involvement of cyclic GMP-dependent and cyclic AMP-dependent protein kinases, protein kinase modulators and cyclic nucleotide phosphodiesterases in functions of vascular tissues were investigated in the dog. All of the above activities, localized in the smooth muscle-rich inner layer of the blood vessels, were found to be higher in the arteries than in the veins. The peripheral arteries were disproportionately richer in cyclic GMP-dependent protein kinase (as indicated by high ratios of cyclic GMP-dependent to cyclic AMP-dependent protein kinase) than were the veins, with the exception of the pulmonary artery, an atypical arterial tissue exposed to low blood pressure. Interestingly, the protein kinase ratio for the aorta, an artery with no significant role in blood pressure regulation, was not higher than that for the vena cava. Creation of femoral arteriovenous fistulae in the dogs led to preferential reductions in the cyclic GMP-dependent enzyme activity both in the proximal and distal arteries, whereas it was elevated in the stressed vein distal to the anastomotic site. The cyclic GMP-dependent enzyme was preferentially reduced in the saphenous artery distal to occlusion. Changes in the cyclic GMP-dependent enzyme activity appeared to precede gross atrophy or hypertrophy of the vessels. It is suggested that the vascular cyclic GMP-dependent protein kinase may be closely related to peripheral resistance and its regulation. 相似文献
25.
Lipid storage in fat-body cells of adult female black flies was examined using freeze-etching electron microscopy. Frozen-etched lipid granules exhibited a laminated structure. The molecular arrangement of the lipid granule may depend on the physiological condition of the insect and may be involved in the control of lipid metabolism in the fat-body cell. 相似文献
26.
S. E. Davies 《BMJ (Clinical research ed.)》1968,3(5618):593-594
In eight patients with exercise-induced asthma, disodium cromoglycate was found to produce a definite inhibition of the post-exercise fall in forced expiratory volume in one second. This effect may be part of the cause for the subjective improvement experienced with this drug. 相似文献
27.
Reports that apoptosis within populations of neurotrophin-dependent neurones is virtually eliminated in BAX-deficient mice and that BAX-deficient neurones survive indefinitely in culture without neurotrophins have led to the view that BAX is required for the death of neurotrophin-deprived neurones. To further examine this assertion in vivo, we have studied two populations of NGF-dependent neurones during the period of naturally occurring neuronal death in mice that lack BAX, NGF or the NGF receptor TrkA, alone and in combination. In the superior cervical ganglion (SCG), naturally occurring neuronal death and the massive loss of neurones that took place in the absence of NGF or TrkA were completely prevented by elimination of BAX. However, in the trigeminal ganglion, naturally occurring neuronal death was only partly abrogated by the elimination of BAX, and although the massive neuronal death that took place in this ganglion in the absence of NGF or TrkA was initially delayed in embryos lacking BAX, this subsequently occurred unabated. Accordingly, BAX-deficient neurones survived in defined without NGF whereas BAX-deficient trigeminal neurones died in the absence of NGF. These results indicate that whereas BAX is required for the death of SCG neurones during normal development and when these neurones are deprived of NGF/TrkA signalling in vivo, the death of trigeminal ganglion neurones occurs independently of BAX when they are deprived of NGF/TrkA signalling. We conclude that BAX is not universally required for neuronal death induced by neurotrophin deprivation, but that there are major differences for the requirement for BAX among different populations of NGF-dependent neurones. 相似文献
28.
Patrick Sullivan 《CMAJ》1987,137(11):1040-1041
29.
In maturing sperm of the winter flounder, histones are not replaced by protamines but instead joined by a group of high molecular weight basic nuclear proteins. Despite their large size and number of components, these proteins were reduced to a relatively simple set of peptides by a "limit" digestion with endoprotease Lys-C. Nine of these peptides, that together account for half of the mass of the digest, were purified by two rounds of chromatography on a C18 reverse-phase high pressure liquid chromatographic column and analysed by sequential Edman degradation. Their sequences can be divided into two homology groups. Seven of the peptides contain all or part of a dodecapeptide consensus sequence, NH2-Ser-Pro-Met-Arg-Ser-Arg-Ser-Pro-Ser-Arg-Ser-Lys-COOH, which appears to be tandemly repeated. This dodecapeptide contains a previously recognized consensus phosphorylation sequence, NH2-Arg-Ser-Arg-Ser-Pro-COOH, in which both serines are phosphorylated during the early stages of spermiogenesis. The other homology group has the sequence NH2-Arg-Arg-Val-X-X-Pro-Lys-COOH, where X-X is either Gln-Thr or Pro-Ser. The dodecapeptide and heptapeptide sequences form at least 35 and 11%, respectively, of the high molecular weight basic nuclear proteins and are, therefore, repeated many times over in these proteins. A search for identical or homologous sequences within the Protein Sequence Database indicated that they are unique. The closest matches were to protamines and some viral DNA-binding proteins. 相似文献
30.