全文获取类型
收费全文 | 145113篇 |
免费 | 7558篇 |
国内免费 | 103篇 |
专业分类
林业 | 6113篇 |
农学 | 4221篇 |
基础科学 | 884篇 |
15844篇 | |
综合类 | 27925篇 |
农作物 | 5572篇 |
水产渔业 | 6618篇 |
畜牧兽医 | 75142篇 |
园艺 | 1651篇 |
植物保护 | 8804篇 |
出版年
2018年 | 1721篇 |
2017年 | 1886篇 |
2016年 | 1761篇 |
2015年 | 1576篇 |
2014年 | 1910篇 |
2013年 | 5159篇 |
2012年 | 3391篇 |
2011年 | 4309篇 |
2010年 | 2755篇 |
2009年 | 2770篇 |
2008年 | 4181篇 |
2007年 | 4051篇 |
2006年 | 3905篇 |
2005年 | 3570篇 |
2004年 | 3448篇 |
2003年 | 3495篇 |
2002年 | 3313篇 |
2001年 | 4394篇 |
2000年 | 4509篇 |
1999年 | 3570篇 |
1998年 | 1365篇 |
1997年 | 1395篇 |
1995年 | 1651篇 |
1994年 | 1410篇 |
1993年 | 1382篇 |
1992年 | 3062篇 |
1991年 | 3235篇 |
1990年 | 3197篇 |
1989年 | 3212篇 |
1988年 | 3000篇 |
1987年 | 3042篇 |
1986年 | 3105篇 |
1985年 | 3021篇 |
1984年 | 2451篇 |
1983年 | 2181篇 |
1982年 | 1484篇 |
1979年 | 2359篇 |
1978年 | 1884篇 |
1977年 | 1655篇 |
1976年 | 1585篇 |
1975年 | 1727篇 |
1974年 | 2228篇 |
1973年 | 2293篇 |
1972年 | 2244篇 |
1971年 | 2091篇 |
1970年 | 1996篇 |
1969年 | 1786篇 |
1968年 | 1546篇 |
1967年 | 1609篇 |
1966年 | 1442篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Shapley H 《Science (New York, N.Y.)》1948,108(2812):553-554
22.
Elftman H 《Science (New York, N.Y.)》1938,88(2276):152-153
23.
24.
25.
26.
27.
28.
M P Yang R Goitsuka H Tsujimoto M Onuma A Hasegawa 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》1992,54(4):757-761
The association of tumor-associated antigen (TAA) on the proliferation of BLV-infected lymphoblastoid B-cell lines (BL2M3 and BL312) was investigated. Flow cytometric analysis of the expression of TAA with monoclonal antibody (mAb) c143 showed high expression of TAA on the surfaces of BL2M3 and BL312 cells. A large amount of TAA was found in the culture supernatant of BL2M3 and BL312 cells as well as in the lysates of BL2M3 and BL312 cells. Culture supernatant but not lysates of BL2M3 and BL312 cells promoted the growth of either BL2M3 cells or BL312 cells. Furthermore, this growth promoting activity in culture supernatants of BL2M3 and BL312 cells was inhibited in a dose-dependent manner when cultured with mAb c143. These results suggested that TAA may be involved in the growth factor-mediated cell growth of bovine B-lymphoblastoid cell lines expressing TAA on their cell surface. 相似文献
29.
Soil pH declined from 5.9 to 5.0 in 8 years beneath plantations of Eucalyptus saligna (Sm.) in Hawaii. In stands of Albizia falcataria, (L.) Fosberg, the soil pH change was more dramatic, declining from 5.9 to 4.6. We measured several components of soil acidity beneath four mixtures of the two tree species to gain insight on the processes responsible for the decline in soil pH. These components were studied using an empirical method of comparing acid quantity, degree of neutralization (depletion of base cations), and acid strength. The decline in soil pH differed between species as a result of differences in the degree of neutralization of the soil exchange complex; the larger decrease in soil pH under Albizia was produced by greater acidification of the exchange complex. Empirical titration curves suggested that differences in acid strength moderated the divergence in soil pH beneath the species. Had the acids accumulating in the soil under Albizia been as strong as those in the Eucalyptus soil, the difference in soil pH would have been greater. Though the two species had contrasting effects on soil pH, the differences in degree of neutralization, responsible for the pH decline, were small compared with differences in the amount of cations stored in tree biomass. Continued supply of nutrient cations (from weathering or fertilization) will ultimately control both the extent of soil pH decline and the level of productivity sustained by the forest. 相似文献
30.
A technique is described for biopsy of the bovine udder, employing sedation and local anaesthesia. Tissue samples of approximately 5 g were obtained by electrocautery from two quarters of the udder of a cow laterally recumbent. Care was taken to ensure complete haemostasis which was achieved by electrocoagulation and ligation. Postoperative recovery was rapid, and loss of yield was no greater in biopsied glands than in control glands of the same cow. Yield from all quarters returned to preoperative levels within 48 h. 相似文献