全文获取类型
收费全文 | 9960篇 |
免费 | 915篇 |
国内免费 | 18篇 |
专业分类
10893篇 |
出版年
2023年 | 44篇 |
2022年 | 113篇 |
2021年 | 170篇 |
2020年 | 125篇 |
2019年 | 158篇 |
2018年 | 219篇 |
2017年 | 211篇 |
2016年 | 289篇 |
2015年 | 511篇 |
2014年 | 529篇 |
2013年 | 638篇 |
2012年 | 785篇 |
2011年 | 708篇 |
2010年 | 470篇 |
2009年 | 443篇 |
2008年 | 617篇 |
2007年 | 559篇 |
2006年 | 502篇 |
2005年 | 454篇 |
2004年 | 423篇 |
2003年 | 389篇 |
2002年 | 358篇 |
2001年 | 196篇 |
2000年 | 181篇 |
1999年 | 144篇 |
1998年 | 92篇 |
1997年 | 71篇 |
1996年 | 55篇 |
1995年 | 83篇 |
1994年 | 47篇 |
1993年 | 57篇 |
1992年 | 91篇 |
1991年 | 76篇 |
1990年 | 85篇 |
1989年 | 86篇 |
1988年 | 86篇 |
1987年 | 78篇 |
1986年 | 67篇 |
1985年 | 79篇 |
1984年 | 54篇 |
1983年 | 45篇 |
1982年 | 37篇 |
1980年 | 31篇 |
1979年 | 49篇 |
1978年 | 46篇 |
1977年 | 31篇 |
1976年 | 43篇 |
1975年 | 39篇 |
1974年 | 36篇 |
1973年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
A novel primase-free form of murine DNA polymerase alpha induced by infection with minute virus of mice 总被引:2,自引:0,他引:2
Two species of DNA polymerase alpha free of primase activity were identified in extracts of Ehrlich mouse cells that had been infected with minute virus of mice. Primase-free forms of DNA polymerase alpha eluted with 150 and 180 mM NaCl during ion-exchange chromatography on DEAE-cellulose columns, exhibited sedimentation coefficients of 11 S and 8.2 S, respectively, and were inhibited by aphidicolin, N2-(p-n-butylphenyl)-9-(2-deoxy-beta-D-ribofuranosyl)guanine 5'-triphosphate, and 2-(p-n-butylanilino)-9-(2-deoxy-beta-D-ribofuranosyl)adenine 5'-triphosphate. The ratio of primase-free DNA polymerase alpha to the DNA polymerase alpha-primase complex increased from 1.5 to greater than 100 during the course of infection, and free primase was produced during the MVM replicative cycle. 相似文献
42.
43.
The primary product of hydrolysis of versiconal acetate catalyzed by porcine liver esterase and the 35–70% ammonium sulfate fraction from a soluble extract from mycelia of Aspergillus parasiticus was versiconal. Versiconal was stable at neutral pH for several hours and was rapidly converted to versi-colorin C by treatment with 0.4 M HCl. The addition of NADPH to the 35–70% ammonium sulfate fraction resulted in conversion of versiconal acetate to both versiconal and versicolorin C. The conversion of versiconal acetate to versicolorin C in the cell-free system is proposed to involve an esterase and an NADPH-dependent cyclase. 相似文献
44.
45.
46.
Gene splicing by overlap extension: tailor-made genes using the polymerase chain reaction 总被引:83,自引:0,他引:83
Gene Splicing by Overlap Extension or "gene SOEing" is a PCR-based method of recombining DNA sequences without reliance on restriction sites and of directly generating mutated DNA fragments in vitro. By modifying the sequences incorporated into the 5'-ends of the primers, any pair of polymerase chain reaction products can be made to share a common sequence at one end. Under polymerase chain reaction conditions, the common sequence allows strands from two different fragments to hybridize to one another, forming an overlap. Extension of this overlap by DNA polymerase yields a recombinant molecule. This powerful and technically simple approach offers many advantages over conventional approaches for manipulating gene sequences. 相似文献
47.
48.
M. Jane Ehrke Richard L. X. Ho Kazuyoshi Hori 《Cancer immunology, immunotherapy : CII》1988,27(2):103-108
Summary Recombinant murine (rMu) tumor necrosis factor (TNF), in a standard comitogenic assay with phytohemagglutinin, induced murine thymocyte proliferation, while up to 10,000-fold higher concentrations of recombinant human TNF did not. The induction of thymocyte proliferation was dependent upon TNF concentration in a biphasic manner. Thus, 100 to 1000 units/ml TNF were near optimal while concentrations 1,000 units/ml caused apparent down regulation. The effect was abrogated by neutralizing antibody to rMu-TNF but not by neutralizing antibody to rMu-interleukin 1 or . The rMu-TNF did not induce proliferation of the mature murine T-helper cell line, D10.G4.1, in the presence of mitogen. Taken together the results indicate that TNF, in a strictly species-specific manner, can regulate thymocyte proliferation independently of interleukin 1.Supported in part by Asahi Chemical Industry Co., Inc. and by USPHS Grants CA-24538, CA-15142 and CA-09072 awarded by the National Cancer Institute, Department of Health and Human Services 相似文献
49.
50.
Summary A simple method is proposed for calculating oxygen pentration depth in immobilized cells by assuming zero order kinetics in the presence of several external oxygen transport resistances. Calculations indicate that typical penetration depths of oxygen for immobilized microbial cells are in the range of 50–200 and those for immobilized or encapsulated animal and plant tissue culture are about 500–1000 . Based on calculations, oxygen transport in microencapsulation and microcarriers for tissue cultures are not transport-limited, but a slight limitation is expected for those in a hollow fiber reactor.Nomenclature as
specific area of a support (cm)
- Bi
Biot number
-
dimensionless
- Cb
oxygen concentration in the bulk liquid (mM)
-
C
b
C
b
*
-Ccr (mM)
- C
b
*
bulk oxygen concentration in equilibrium with air (mM)
- Ccr
critical oxygen concentration (mM)
- Cs
oxygen concentration in the solid phase (mM)
- dp
diameter or thickness of a support (cm)
- Deff
effective diffusivity of oxygen in the solid phase (cm2/s)
- km
membrane permeability of oxygen (cm/s)
- k
m
*
Deff/m
- kLaL
liquid phase mass transfer rate coefficient (1/s)
- ksas
solid phase mass transfer rate coefficient (1/s)
- (OUR)v
volumetric oxygen uptake rate (mmol O2/l)
- p
geometry parameter, p=0 for slab, p=1 for cylinder, p=2 for sphere
- Pd
oxygen penetration depth (cm)
-
P
d
oxygen penetration depth in the absence of external diffusion limitation (cm)
- Q
volumetric oxygen uptake rate,
(mmol O2/l·h)
-
specific oxygen uptake rate (mmol O2gm biomass (dry)·h)
- r
length coordinate (cm)
- rc
oxygen penetration depth for sphere (cm)
-
r
c
rc in the absence of external diffusion limitation (cm)
- r
c
*
oxygen penetration depth for cylinder (cm)
-
r
c
*
r
c
*
in the absence of external diffusion limitation (cm)
- rcom
combined mass transfer rate resistance (s)
- rd
location where Cs becomes zero or Ccr (cm)
- ri
radius of cylinder or sphere, half thickness of slab (cm)
- Usg
superficial gas velocity (cm/s)
- X
cell concentration (g/l)
Greek letters
Thiele modulus, dimensionless
- L, s
liquid and solid phase volume fraction, respectively, dimensionless
-
effectiveness factor
On sabbatical leave from KAIST, Seoul, Korea 相似文献