全文获取类型
收费全文 | 77517篇 |
免费 | 6053篇 |
国内免费 | 5209篇 |
出版年
2024年 | 130篇 |
2023年 | 942篇 |
2022年 | 2232篇 |
2021年 | 3809篇 |
2020年 | 2474篇 |
2019年 | 3177篇 |
2018年 | 2940篇 |
2017年 | 2191篇 |
2016年 | 3214篇 |
2015年 | 4568篇 |
2014年 | 5513篇 |
2013年 | 5990篇 |
2012年 | 6810篇 |
2011年 | 6394篇 |
2010年 | 3733篇 |
2009年 | 3447篇 |
2008年 | 4010篇 |
2007年 | 3584篇 |
2006年 | 3044篇 |
2005年 | 2555篇 |
2004年 | 2119篇 |
2003年 | 1987篇 |
2002年 | 1595篇 |
2001年 | 1467篇 |
2000年 | 1314篇 |
1999年 | 1269篇 |
1998年 | 765篇 |
1997年 | 771篇 |
1996年 | 760篇 |
1995年 | 669篇 |
1994年 | 626篇 |
1993年 | 480篇 |
1992年 | 676篇 |
1991年 | 588篇 |
1990年 | 474篇 |
1989年 | 371篇 |
1988年 | 327篇 |
1987年 | 279篇 |
1986年 | 190篇 |
1985年 | 236篇 |
1984年 | 154篇 |
1983年 | 143篇 |
1982年 | 97篇 |
1981年 | 77篇 |
1980年 | 63篇 |
1979年 | 76篇 |
1978年 | 66篇 |
1977年 | 46篇 |
1976年 | 48篇 |
1973年 | 48篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
972.
Localization of the gene for the DNA-binding protein AP-2 to human chromosome 6p22.3-pter 总被引:4,自引:0,他引:4
R B Gaynor C Muchardt Y R Xia I Klisak T Mohandas R S Sparkes A J Lusis 《Genomics》1991,10(4):1100-1102
973.
Comparison of amide proton exchange in reduced and oxidizedRhodobacter capsulatus cytochrome c2: A1H−15N NMR study 总被引:6,自引:0,他引:6
Summary The hydrogen-deuterium exchange rates of the reduced and oxidized forms ofRhodobacter' capsulatus cytochrome c2 were studied by1H–15N homonuclear multiple quantum correlation spectroscopy. Minimal differences were observed for the N- and C-terminal helices on changing redox state suggesting that although these helices are structurally important they do not affect the relative stability of the two redox states and hence may not be important in determining the redox potential differences observed amongst the class I c-type cytochromes. However, significant differences were observed for other regions of the protein. For example, all slow exchanging protons of the helix spanning Phe82 to Asp87 are similarly affected on reduction indicating that the unfolding equilibrium of this helix is altered between the two redox states. Other regions are not as simple to interpret; however, the difference in NH exchange rates between the redox states for a number of residues including His17, Leu37, Arg43, Ala45, Gly46, Ile57, Val58, Leu60, Gly61 and Leu100 suggest that interactions affecting the causes of these differences may be important factors in determining redox potential.Abbreviations NMR
nuclear magnetic resonance
- HMQC
homonuclear multiple quantum correlation
- NOESY
nuclear Overhauser effect spectroscopy 相似文献
974.
Summary An Enzyme Linked Immuno Sorbent Assays (ELISA) and an Electro-chemiluminescent Immuno Assay (CIA) are compared for the purpose of monitoring product formation in mammalian cell bioreactors. The ELISA had a relative standard deviation of 10%, compared to 8% for the CIA . The CIA was found to be a fast and accurate alternative to the ELISA. The use of more than one immuno assay format was also shown to provide additional insight into process performance. 相似文献
975.
976.
977.
978.
Cultivation of Brevibacterium divaricatum for glutamic acid production in an airlift reactor with net draft tube was developed. Cell concentration gave an index for adding penicillin G. On-line estimation of total sugar concentration yielded an identified model which was used for determination of the substrate addition. Fermentation for glutamic acid production requires high oxygen concentration in the broth. The proposed reactor has the capability to provide sufficient oxygen for the fermentation. Since the reactor is suitable for fed-batch culture, the cultivation of B. divaricatum for glutamic acid production in the proposed reactor is successfully carried out.List of Symbols
a
system parameter
-
b
system parameter
-
C
c,in
mole fraction carbon dioxide in the gas inlet
-
C
c,out
mole fraction carbon dioxide in the gas outlet
-
C
L
mole/dm3
oxygen concentration in liquid phase
-
C
L
*
mole/dm3
saturated oxygen concentration in liquid phase
-
C
0,in
mole fraction of oxygen in the gas inlet
-
C
0,out
mole fraction of oxygen in the gas outlet
-
CPR mole/h/dm3
carbon dioxide production rate based on total broth
-
E(t)
error signal
-
F
in
mole/h
inlet gas flow rate
-
k
1
constant defined by Eq. (4)
-
k
2
constant defined by Eq. (5)
-
k
L
a 1/h
volumetric mass transfer coefficient of gas-liquid phase
-
OUR mole/h/dm3
oxygen uptake rate based on total broth
-
P atm
pressure in the reactor
-
t h
time
-
TS
c
g
total sugar consumption
-
TS
s
g/dm3
set point of total sugar concentration
-
TS
*
g/dm3
reference value of total sugar concentration
-
TS(t) g/dm3
total sugar concentration in the broth at timet
-
u(t) cm3/min
feed rate at timet
-
V dm3
total broth volume
-
VVM (dm3/min)/dm3
flow rate per unit liquid volume
-
a negative constant defined by Eq. (7) 相似文献
979.
中国野生牡丹研究(一)芍药属牡丹组新分类群 总被引:44,自引:0,他引:44
牡丹为我国特产珍贵花树和药用树种,已有1500余年栽培历史,建国以来,各地栽培品种已达500余个。 有关牡丹分类的主要研究成果多为西方科学家根据18—19世纪从我国引种到英、美、法等国的栽培牡丹和腊叶标本加以描述和定名。 作者近几年来在安徽、河南、湖南、山西、陕西、甘肃、四川、云南等地对我国野生牡丹进行了较广泛的调查和研究。 本文发表3个新种和1个新等级,这对研究我国栽培牡丹的起源和栽培品种的自然分类,发掘、保护、利用我国珍稀野生牡丹基因资源,培育新品种,扩大牡丹栽培地区等方面提供了科学理论依据。 相似文献
980.
多效唑连用其它植物激素对水稻试管苗生长的影响 总被引:3,自引:0,他引:3
本实验采用继代多年的花培体细胞无性系Hu18再生绿芽(0.5mm)为起始材料,研究多效唑(MET)与其它激素配合使用对试管苗的调控作用,结果指出:(1)单独使用MET对绿芽生长有毒害作用,除2,4-D、GA,外,MET与适宜浓度的其它激素配合使用才能发挥增苗、壮苗作用,其中以MET与BA配合使用的培养效果最好,MET与NAA,C_2H_4配合使用的效果次之;(2)MET与其他激素配合使用不但能降低植株高度,促进根系发育,而且可以延长试管苗的保存时间;(3)MET与乙烯利配合使用能加速绿芽成苗速度,而与其他激素配合使则延缓绿芽成苗速度,如与2,4-D配合使用则延缓2,4-D对绿芽的脱分化进程;(4)在本实验条件下,以MET 2.5mg/L+BA 2mg/L+NAA 0.2mg/L配合使用有利根芽的协调生长。本文还从植株干物质累积,叶细胞结构,细胞活力等方面进行了探讨。 相似文献