全文获取类型
收费全文 | 6702篇 |
免费 | 729篇 |
国内免费 | 9篇 |
出版年
2021年 | 56篇 |
2018年 | 64篇 |
2016年 | 79篇 |
2015年 | 117篇 |
2014年 | 155篇 |
2013年 | 197篇 |
2012年 | 229篇 |
2011年 | 256篇 |
2010年 | 196篇 |
2009年 | 156篇 |
2008年 | 249篇 |
2007年 | 267篇 |
2006年 | 224篇 |
2005年 | 280篇 |
2004年 | 224篇 |
2003年 | 246篇 |
2002年 | 272篇 |
2001年 | 120篇 |
2000年 | 128篇 |
1999年 | 121篇 |
1998年 | 76篇 |
1997年 | 76篇 |
1996年 | 71篇 |
1995年 | 63篇 |
1994年 | 72篇 |
1993年 | 77篇 |
1992年 | 79篇 |
1991年 | 82篇 |
1990年 | 72篇 |
1989年 | 83篇 |
1988年 | 79篇 |
1987年 | 77篇 |
1986年 | 77篇 |
1985年 | 93篇 |
1984年 | 122篇 |
1983年 | 99篇 |
1982年 | 157篇 |
1981年 | 147篇 |
1980年 | 121篇 |
1979年 | 98篇 |
1978年 | 80篇 |
1977年 | 57篇 |
1976年 | 93篇 |
1975年 | 80篇 |
1974年 | 76篇 |
1973年 | 103篇 |
1972年 | 67篇 |
1971年 | 66篇 |
1970年 | 58篇 |
1968年 | 62篇 |
排序方式: 共有7440条查询结果,搜索用时 46 毫秒
1.
2.
3.
4.
Plants of four isolines of soyabean [Glycine max(L.) Merrill]Clark, vizL71-920 (maturity genecomplemente1e2e3 ), L80-5914 (E1e2e3), Clark(e1E2E3), and L65-3366 (E1E2E3), were grown inshort (12.25 h d - 1natural light) and long days (12.25 h d- 1natural light supplemented with 2.75 h d - 1low-irradianceartificial light) from first flowering to maturity in a polythenetunnel maintained at 30/24°C (day/night). Whereas therewere few differences among the isolines grown in short days,in long days the dominant alleles increased crop duration, biomassand seed yield substantially. Increases in biological and economicyield were not solely a consequence of longer crop duration:the dominant alleles also increased crop growth rate and radiationuse efficiency in long days (from 1.3 g MJ - 1total radiationine1e2e3 to 2.8 g MJ - 1inE1E2E3 ). Greater radiation use efficiencyresulted from a relatively longer leaf area duration, betterdistribution and orientation of a larger mass of leaves withinthe canopy, and smaller partitioning of assimilates to reproductivestructures. The work reveals the substantial effects of thethree lociE1 / e1, E2/ e2and E3/e3 on the response of plantgrowth, as well as development, to environment. Their relevanceto crop adaptation is discussed. Copyright 2000 Annals of BotanyCompany Glycine max(L.) Merrill, soyabean, maturity genes, flowering, phenology, growth, yield 相似文献
5.
Two varieties of grain sorghum were harvested at 10 intervals from 35–189 days post planting. Leaf, stem and head portions were separated before being prepared for chemical analysis or ensiled for 30 days in 1-1 silos with or without preservatives. The taller variety (FS-1b) accumulated 60% more dry matter than ORO-T with advancing plant maturity, while whole plant crude protein content decreased from near 20 to less than 7% for both varieties. Dry matter ensiling loss (DMEL) was different (P < 0.05) for each plant portion, but was lower and less variable after the 77-day harvest. Immature leaves and heads resulted in the greatest average DMEL of 31 and 24%, respectively. Propionic acid decreased DMEL, while an ammonia solution was ineffective when compared to control leaf, stem and heads. The DMEL of leaves was influenced (P < 0.05) by a varietal × modulus of fineness interaction while the stem exhibited an interaction with plant maturity × modulus of fineness. Modulus of fineness was not associated with levels of organic acid production in silages, but plant maturity significantly influenced acetic, propionic and butyric acid production in heads. These data indicated that numerous combinations of silage preservation techniques affected DMEL of sorghum plant portions at different maturities. 相似文献
6.
Thorsten Thye Genevieve Scarisbrick Edmund N. L. Browne Margaret Amanua Chinbuah John Gyapong Ivy Osei Ellis Owusu-Dabo Stefan Niemann Sabine Rüsch-Gerdes Christian G. Meyer Rolf D. Horstmann 《PloS one》2009,4(7)
The gene of Cytotoxic T Lymphocyte-associated Antigen 4 (CTLA4), a negative regulator of T lymphocytes, contains a single-nucleotide polymorphism (SNP) at position +6230A->G (ct60A->G), which has been found associated with several autoimmune diseases and appears to reduce T-cell inhibitory activity. In Ghana, West Africa, we compared the frequencies of CTLA4 +6230 A/G and 6 haplotype-tagging SNPs in 2010 smear-positive, HIV-negative patients with pulmonary tuberculosis (TB) and 2346 controls matched for age, gender and ethnicity. We found no difference in allele frequencies between cases and controls. However, +6230A and a distinct CTLA4 haplotype and a diplotype comprising the +6230A allele were significantly less frequent among cases with large opacities in chest radiographs compared to those with small ones (Pcorrected [cor] = 0.002, Pcor = 0.00045, P = 0.0005, respectively). This finding suggests that an increased T-cell activity associated with the CTLA4 +6230G allele contributes to pathology rather than to protection in pulmonary TB. 相似文献
7.
Harold Chapple 《BMJ (Clinical research ed.)》1945,1(4401):661-662
8.
Harold Dodd 《BMJ (Clinical research ed.)》1944,2(4381):814-816
9.
Ferdinand Bohlmann Elena Tsankova Jasmin Jakupovic Robert M. King Harold Robinson 《Phytochemistry》1983,22(2):557-560
The investigation of Encelia canescens afforded, in addition to several known compounds, four new dimeric p-hydroxyacetophenone derivatives, two epimeric chromene dimers and two epimeric mixed dimers of euparin and encecalin. Furthermore, derivatives of tremetone and of encecalin were present. The structures were elucidated hy high field 1H NMR spectroscopy. 相似文献
10.