全文获取类型
收费全文 | 2716篇 |
免费 | 201篇 |
国内免费 | 203篇 |
出版年
2023年 | 33篇 |
2022年 | 33篇 |
2021年 | 75篇 |
2020年 | 67篇 |
2019年 | 79篇 |
2018年 | 71篇 |
2017年 | 68篇 |
2016年 | 91篇 |
2015年 | 80篇 |
2014年 | 183篇 |
2013年 | 206篇 |
2012年 | 131篇 |
2011年 | 120篇 |
2010年 | 109篇 |
2009年 | 138篇 |
2008年 | 129篇 |
2007年 | 136篇 |
2006年 | 125篇 |
2005年 | 124篇 |
2004年 | 93篇 |
2003年 | 88篇 |
2002年 | 76篇 |
2001年 | 70篇 |
2000年 | 57篇 |
1999年 | 61篇 |
1998年 | 49篇 |
1997年 | 47篇 |
1996年 | 39篇 |
1995年 | 61篇 |
1994年 | 37篇 |
1993年 | 32篇 |
1992年 | 36篇 |
1991年 | 26篇 |
1990年 | 32篇 |
1989年 | 29篇 |
1988年 | 33篇 |
1987年 | 31篇 |
1986年 | 26篇 |
1985年 | 29篇 |
1984年 | 33篇 |
1983年 | 18篇 |
1982年 | 14篇 |
1981年 | 23篇 |
1980年 | 17篇 |
1979年 | 18篇 |
1978年 | 8篇 |
1977年 | 9篇 |
1975年 | 5篇 |
1974年 | 8篇 |
1973年 | 6篇 |
排序方式: 共有3120条查询结果,搜索用时 78 毫秒
71.
蓟属两种植物的染色体研究 总被引:2,自引:0,他引:2
本文对蓟属(Cirsium)的两个形态相似的近缘种大刺儿菜和小刺儿菜进行了染色体研究,其中后者为首次报道。观察结果表明:两个种的染色体数目均为2n=2x=34:它们的核型是:大刺儿菜.2n=2x=34=20m+12sm+2st:小刺儿菜.2n=2x=34=22m+10km(2SAT)+2st。通过核型比较,认为它们是两个独立的种.而且后者比前者进化。 相似文献
72.
73.
The chick oviduct in tissue culture. I. Initial characterization of growing primary oviduct tissue cultures 总被引:1,自引:0,他引:1
A simple three-enzyme treatment of collagenase, dispase and hyaluronidase on finely minced chick oviduct yields clumps of 50-150 cells. These cells attach to collagen-treated dishes and survive in culture for at least 2 weeks without subculturing. Oviduct cell cultures can also be induced to grow. Estradiol or epidermal growth factor (EGF) induce a 40% increase in cells in 4 days when cultures are grown in serum levels that do not support growth. Serum from estrogen-stimulated chicks promotes rapid cellular proliferation (doubling times of 1-2 days). Sera from estrogen withdrawn chicks, laying hen or horse do not support as rapid proliferation. The oviduct growth-promoting factors in serum from estrogen-stimulated chicks are not steroids or fibroblast growth factors (FGF). Removal of steroids from these sera by charcoal treatment or delipidization does not decrease the rate of growth. The addition of 1-100 nM estradiol does not increase a serum's ability to promote growth. Purified FGF or platelet-derived growth factor (PDGF) do not induce oviduct proliferation. These results were reproduced in oviduct cell cultures started from estrogen-stimulated and withdrawn chicks as well as laying hens. Thus the factors in serum from estrogen-stimulated chicks that promote rapid oviduct growth are induced by estrogen treatments in vivo, but do not seem to be only steroids. 相似文献
74.
75.
76.
George J. P. Murphy 《Planta》1980,149(5):417-426
Naphthalene-1-acetic acid (NAA) binding by membrane fractions derived from maize has been re-evaluated. Using a computer curve-fitting procedure only one major type of NAA binding, in terms of binding affinity, could be identified. Auxins, antiauxins and structurally related compounds have been tested for their competitive effect on NAA binding and the inhibitor constants for a number of these have been determined. Extracts from various plant species have been examined for their NAA binding ability, but all showed much less binding than maize leaf or coleoptile preparations. The possibility of the NAA binding by maize extracts being due to a true hormone receptor is discussed.Abbreviations BA
benzoic acid
- CPIB
p-chlorophenoxyisobutyric acid
- 2,4-D
2,4-dichlorophenoxyacetic acid
- DCB
2,4-dichlorobenzoic acid
- IAA
indolyl-3-acetic acid
- NAA
napthalene-1-acetic acid
- 2-NAA
napthalene-2-acetic acid
- NAOA
napthalene-2-oxyacetic acid
- PA
phenylacetic acid
- PU
phenylurea
- 2,4,5-T
2,4,5-trichlorophenoxyacetic acid
- TIBA
2,3,5-triiodobenzoic acid 相似文献
77.
78.
J. J. González-Aguilera A. Ma. Fernández-Peralta 《Plant Systematics and Evolution》1981,139(1-2):147-154
The meiotic behaviour abnormalities, fertility and size of pollen of 6 taxa ofSesamoides have been analysed. Besides diploids (2x), polyploids (4x, 6x, 8x) have been found. The chromosome base number is x = 10, but an origin from x = 5 is suggested. 相似文献
79.
We have investigated the interaction of VIP and secretin with two human lung carcinoma cell lines in cultures, SW-900 and Calu-1. 125I-labeled VIP binds to and is inactivated by SW-900 and Calu-1 cells in a time- and temperature-dependent manner. The rates of binding and of inactivation were higher at 30°C than at 15°C. At equilibrium, native VIP competitively inhibited the binding of 125I-VIP in the 10?10?10?7M range, half-maximal inhibition being observed at 1.2 nM in SW-900 cells and at 1.1 nM VIP in Calu-1 cells. Scatchard analysis indicated two classes of binding sites with similar characteristics in both cell lines. SW-900 cells have 27 600 sites with a high affinity () and 1062 000 sites with a low affinity (). Calu-1 cells have 36 300 sites with a high affinity () and 1148 000 sites with a low affinity (). Secretin inhibited tracer binding but with a 5000 times lower potency than native VIP in both cell lines. 相似文献
80.
Margit M.K. Nass 《Gene》1983,21(3):249-255
A precise physical map, containing the structurally and operationally defined D-loop origin, terminal region, and direction of heavy-strand replication, has been constructed for mitochondrial DNA (mtDNA) from ovary (CHO-KI) and lung cells of Chinese hamster (Cricetulus griseus 2 N = 22), and compared with our previously established genome coordinates for mtDNA from Syrian hamster ( Mesocricetus auratus 2 N = 44). All four HpaI sites in Cricetulus are conserved in Mesocricetus (8 sites). Extensive variation exists for hexanucleotides cleaved by EcoRI HindIII PstI. KpnI and BamHI. Sequence divergence between Chinese and Syrian hamster mtDNAs, as reflected from analysis of the mapped recognition sites for these six endonucleases, is estimated as 5–9% base substitutions. mtDNAs from both hamster and several other mammalian species contain a commonly conserved HpaI site in the region of light strand initiation. 相似文献