全文获取类型
收费全文 | 36125篇 |
免费 | 3586篇 |
国内免费 | 2080篇 |
出版年
2023年 | 339篇 |
2022年 | 414篇 |
2021年 | 1338篇 |
2020年 | 983篇 |
2019年 | 1205篇 |
2018年 | 1194篇 |
2017年 | 923篇 |
2016年 | 1322篇 |
2015年 | 1904篇 |
2014年 | 2231篇 |
2013年 | 2377篇 |
2012年 | 2908篇 |
2011年 | 2541篇 |
2010年 | 1633篇 |
2009年 | 1387篇 |
2008年 | 1840篇 |
2007年 | 1594篇 |
2006年 | 1418篇 |
2005年 | 1234篇 |
2004年 | 1066篇 |
2003年 | 929篇 |
2002年 | 845篇 |
2001年 | 1573篇 |
2000年 | 1323篇 |
1999年 | 1118篇 |
1998年 | 457篇 |
1997年 | 431篇 |
1996年 | 407篇 |
1995年 | 347篇 |
1994年 | 401篇 |
1993年 | 255篇 |
1992年 | 570篇 |
1991年 | 488篇 |
1990年 | 441篇 |
1989年 | 327篇 |
1988年 | 278篇 |
1987年 | 210篇 |
1986年 | 193篇 |
1985年 | 171篇 |
1984年 | 110篇 |
1983年 | 102篇 |
1982年 | 64篇 |
1981年 | 52篇 |
1979年 | 63篇 |
1978年 | 44篇 |
1976年 | 53篇 |
1975年 | 50篇 |
1973年 | 56篇 |
1972年 | 59篇 |
1971年 | 54篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Single Cell Transcriptome Amplification with MALBAC 总被引:1,自引:0,他引:1
2.
3.
One new genus of the spider subfamily Coelotinae, Flexicoelotes
gen. n., with five new species is described from southern China: Flexicoelotes
huyunensis
sp. n. (female), Flexicoelotes
jiaohanyanensis
sp. n. (male and female), Flexicoelotes
jinlongyanensis
sp. n. (male and female), Flexicoelotes
pingzhaiensis
sp. n. (female), Flexicoelotes
xingwangensis
sp. n. (male and female). 相似文献
4.
5.
6.
7.
Three saponins from Oxytropis species. 总被引:2,自引:0,他引:2
Three flavonoids and three saponins have been isolated from Oxytropis species. Their structures were determined as isorhamnetin-3-O-beta-D-glucoside, rhamnetin-3-O-beta-D-galactoside, apigenin, 3-O-[alpha-L-rhamnopyranosyl (1----2)-beta-D-glucopyranosyl(1----4)-beta-D-glucuronopyranosyl]+ ++soyasapogenol B, 3-O-[beta-D-glucopyranosyl(1----2)-beta-D-glucuronopyranosyl] azukisapogenol and a new saponin 3-O-[beta-D-glucopyranosyl(1----2)-beta-D-glucopyranosyl]-25-O-alpha-L- rhamnopyranosyl-(20S,24S)-3 beta,16 beta, 20,24,25-pentahydroxy-9,19-cycloanostane. 相似文献
8.
W. D. Roof H. Q. Fang K. D. Young Jianling Sun & Ry Young 《Molecular microbiology》1997,25(6):1031-1046
slyD encodes a 196 amino acid polypeptide that is a member of the FKBP family of cis–trans peptidyl–prolyl isomerases (PPIases). slyD mutations affect plaque formation by the phage φX174 by blocking the action of the phage lysis protein E. Here we describe the selection of a set of spontaneous slyD mutations conferring resistance to the expression of gene E from a plasmid. These mutations occur disproportionately in residues of SlyD that, based on the structure of the prototype mammalian FKBP12, make ligand contacts with immunosuppressing drug molecules or are conserved in other FKBP proteins. A wide variation in the plating efficiency of φX174 on these E R strains is observed, relative to the parental, indicating that these alleles differ widely in residual SlyD activity. Moreover, it is found that slyD mutations cause significant growth rate defects in Escherichia coli B and C backgrounds. Finally, overexpression of slyD causes filamentation of the host. Thus, among the FKBP genes found in organisms across the evolutionary spectrum, slyD is unique in having three distinct drug-independent phenotypes. 相似文献
9.
The high potential heme site of Pseudomonas cytochrome c peroxidase has His and Met as ligands. On reduction, the Fe-met bond becomes photosensitive. Following photolysis, the bond reforms with a half-time of 35 ps. The low potential heme peroxidatic site of the fully reduced enzyme has been shown to bind to a range of ligands. The compounds with carbon monoxide, methyl, ethyl, n-butyl, and t-butyl isonitriles have been investigated by laser flash photolysis. All are photosensitive and show different degrees of geminate recombination of ligand in the picosecond and nanosecond time ranges. Carbon monoxide shows the least effect. The three straight-chain isonitriles show about 50% geminate recombination with half-times of the order of 10 ns. t-Butyl isonitrile shows more and faster recombination. These results imply considerable freedom of movement within the active site for the smaller ligands. 相似文献
10.
Norma Diaz-Gustavo Martín Martínez-Salvador José Luís García-Hernández Mariano Norzagaray-Campos Antonio Luna-González Héctor Abelardo González-Ocampo 《PloS one》2015,10(5)
Caesalpinia platyloba was evaluated as an alternative for the retention of atmospheric carbon and as a feasible and viable economic activity in terms of income for tropical deciduous forest (TDF) peasants in the carbon markets. A total of 110 trees of C. platyloba from plantations and a TDF in the Northwest of Mexico were sampled. Growth (increase in height, diameter, and volume curves) was adjusted to assess their growth. Growth of individuals (height, diameter at breast height [DBH], age, and tree crown cover) was recorded. The Schumacher model (H = β0eβ1•E-1), by means of the guided curve method, was used to adjust growth models. Information analysis was made through the non-linear procedure with the multivariate secant or false position (DUD) method using the SAS software. Growth and increase models revealed acceptable adjustments (pseudo R2>0.8). C. platyloba reaches >8m of height with 12cm in diameter and 550cm3 of volume, presenting the highest increase at 11 years considered as basal age. Highest significant density of wood was in good quality sites (0.80g•cm-3), with a carbon content (average of 99.15tC•ha-1) at the highest density of 2500 trees•ha-1 (without thinning). Average incomes of US$483.33tC•ha-1 are expected. The profitability values (NPW = US$81,646.65, IRR = 472%, and B/C = 0.82) for C. platyloba make its cultivation a viable and profitable activity, considering a management scheme of the income derived from wood selling and from carbon credits. 相似文献