全文获取类型
收费全文 | 9724篇 |
免费 | 599篇 |
国内免费 | 2篇 |
出版年
2023年 | 85篇 |
2022年 | 156篇 |
2021年 | 291篇 |
2020年 | 188篇 |
2019年 | 239篇 |
2018年 | 315篇 |
2017年 | 266篇 |
2016年 | 358篇 |
2015年 | 576篇 |
2014年 | 555篇 |
2013年 | 729篇 |
2012年 | 791篇 |
2011年 | 787篇 |
2010年 | 449篇 |
2009年 | 418篇 |
2008年 | 513篇 |
2007年 | 513篇 |
2006年 | 477篇 |
2005年 | 406篇 |
2004年 | 333篇 |
2003年 | 332篇 |
2002年 | 277篇 |
2001年 | 147篇 |
2000年 | 123篇 |
1999年 | 97篇 |
1998年 | 77篇 |
1997年 | 58篇 |
1996年 | 46篇 |
1995年 | 45篇 |
1994年 | 39篇 |
1993年 | 47篇 |
1992年 | 48篇 |
1991年 | 34篇 |
1990年 | 33篇 |
1989年 | 39篇 |
1988年 | 27篇 |
1987年 | 28篇 |
1986年 | 33篇 |
1985年 | 28篇 |
1984年 | 29篇 |
1983年 | 22篇 |
1982年 | 28篇 |
1981年 | 21篇 |
1980年 | 18篇 |
1979年 | 28篇 |
1978年 | 15篇 |
1977年 | 12篇 |
1976年 | 13篇 |
1975年 | 17篇 |
1974年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
A cDNA probe for the low density lipoprotein (LDL) receptor gene was used to screen DNA samples from 52 unrelated Finnish patients with the heterozygous form of familial hypercholesterolemia (FH) and 51 healthy controls. Southern blot analysis using the restriction enzyme PvuII revealed an abnormal 11 kb (kilo base-pair) restriction fragment in 16 (31%) of the patients but none of the controls. A more detailed restriction enzyme analysis of the DNA from patients revealed a mutation which apparently is due to an 8 kb deletion extending from intron 15 to exon 18 of the LDL receptor gene. Co-segregation of FH with the mutated gene was demonstrated in three families. These data are consistent with a ‘founder gene effect’ and support the assumption that recombinant DNA methods may have great impact on the diagnostics of FH in genetically homogeneous populations. 相似文献
32.
33.
34.
35.
Summary A pot experiment with lettuce involving three N forms each at six application levels, showed that lettuce can be grown satisfactorily
with a very low nitrate content when supplied with ammonium sulphate and a nitrification inhibitor. For plants growing on
nitrate N, the optimum midrib sap nitrate concentration as maturity approached was about 1400 mg/1 NO3-N. Large losses of mineral N were observed from the peat medium, even in the absence of plants.
A relationship is presented which would enable a lettuce grower to estimate whole-shoot nitrate concentration from a quick
test of midrib sapi.e. NO3-N (mg/kg in fresh shoot) =0.14×NO3-N (mg/l in sap).
Tipburn was worst at intermediate levels of applied N, and was less serious with pure ammonium nutrition than with nitrate. 相似文献
36.
Data are presented on the aboveground and underground biomass of the speciesMarsilea quadrifolia and on the water regime and soil conditions in a habitat of this species in Central Europe (Czechoslovakia). 相似文献
37.
Summary Collections over four years in the habitat of submerged litter show that shrimps are abundant the year round. Mean densities vary from 5–45 animals/m2 of litter habitat. Finegrained density distribution within litter sites is highly clumped, but coarse-grained distribution in any given month between litter sites along the river is grosso-modo random.Density and species distribution are a function of the annual cycles of inundations. Of the five species (of a total of seven in the area) that were found to be breeding in the litter habitat it could be established that reproduction is restricted to the period of rising and highest water levels. Reproduction is low in all species, namely below 20 eggs per egg batch with essentially a single generation per year.Breeding ecology in relation to the litter habitat is briefly discussed.This project was supported jointly by the CNPq (Brasilian Research Council), by the OAS (Organization of the American States) and by the SUFRAMA (Financing body of local government) 相似文献
38.
Heikki O. Laurila Helena Nevalainen Veijo Mäkinen 《Applied microbiology and biotechnology》1985,21(3-4):210-212
Summary Protoplast formation in Curvularia inaequalis was achieved using non-commercial and commercial snail gut enzymes or Trichoderma harzianum enzymes. The cells were grown for enzyme treatment on cellophane sheets or in liquid cultures for varying periods of time. The production of T. harzianum enzymes is discussed. The highest protoplast yields were 2.6x107 protoplasts/ml enzyme solution. Protoplasts were shown to have zero to four nuclei. Protoplast regeneration was succesfully carried out in semisolid agar. 相似文献
39.
A J de Araújo L F Ferreira U E Confalonieri L Nu?ez B M Ribeiro Filho 《Memórias do Instituto Oswaldo Cruz》1985,80(2):141-143
Enterobius vermicularis eggs were found in human coprolites collected in the archaeological site of Caserones, Tarapaca Valley, Chile, dating from 400 BC to 800 AD. The human pinworm had already been found in other pre-historic archaeological sites in America, and its introduction in this continent is discussed. 相似文献
40.