全文获取类型
收费全文 | 33543篇 |
免费 | 1001篇 |
国内免费 | 1510篇 |
专业分类
系统科学 | 1151篇 |
丛书文集 | 1297篇 |
教育与普及 | 1337篇 |
理论与方法论 | 135篇 |
现状及发展 | 197篇 |
研究方法 | 119篇 |
综合类 | 31813篇 |
自然研究 | 5篇 |
出版年
2024年 | 235篇 |
2023年 | 463篇 |
2022年 | 633篇 |
2021年 | 767篇 |
2020年 | 435篇 |
2019年 | 172篇 |
2018年 | 289篇 |
2017年 | 376篇 |
2016年 | 364篇 |
2015年 | 754篇 |
2014年 | 1066篇 |
2013年 | 974篇 |
2012年 | 1178篇 |
2011年 | 1278篇 |
2010年 | 1248篇 |
2009年 | 1411篇 |
2008年 | 1506篇 |
2007年 | 1577篇 |
2006年 | 1251篇 |
2005年 | 1288篇 |
2004年 | 860篇 |
2003年 | 748篇 |
2002年 | 704篇 |
2001年 | 860篇 |
2000年 | 993篇 |
1999年 | 1905篇 |
1998年 | 1617篇 |
1997年 | 1725篇 |
1996年 | 1587篇 |
1995年 | 1359篇 |
1994年 | 1199篇 |
1993年 | 1063篇 |
1992年 | 895篇 |
1991年 | 811篇 |
1990年 | 718篇 |
1989年 | 629篇 |
1988年 | 516篇 |
1987年 | 319篇 |
1986年 | 170篇 |
1985年 | 63篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1981年 | 3篇 |
1980年 | 5篇 |
1974年 | 2篇 |
1973年 | 7篇 |
1970年 | 3篇 |
1967年 | 2篇 |
1964年 | 2篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
182.
183.
取食天然饲料与人工饲料的大蜡螟Galleria mellonella的生长发育差异比较 总被引:1,自引:0,他引:1
在温度为35±1℃、相对湿度为65±5%及全黑暗的条件下,对取食天然饲料和人工饲料的大蜡螟Galleria mellonella(L.)的生长发育进行了观察。在天然饲料中,以中蜂巢脾为食的大蜡螟生长发育最好,意蜂巢脾次之,蜂蜡不能很好地使大蜡螟完成发育。试验采用来源广泛且价格低廉的麸糠、面粉和玉米粉为主要原料配制成人工饲料供大蜡螟取食,与供食中蜂巢脾的大蜡螟比较,蛹重、成虫寿命、产卵量均无显著差异,但幼虫历期明显缩短6.8天。 相似文献
184.
Under 2 100 bar of hydrostatic pressure, KNA N-glycosidase can still cleave the N-C bond of adenosine at position 4324 in
R/S domain of 28S RNA in rat ribosome, demonstrating that high pressure has no effect on the tertiary structure of S/R domain. 相似文献
185.
The evolution of methane carbon isotope with depth has been discussed based on diagenetic reaction kinetics and isotopic Rayleigh
fractionational theory. A mathematical model to describe data of methane carbon isotope for the Liaohe oil field has been
established. 相似文献
186.
Discovery and character of the Kunlun-Yellow River Movement 总被引:2,自引:0,他引:2
Based on geomorphological, tectonic and sedimentary data, a Kunlun Yellow River Tectonic Movement has been recognized in 1 10-0 60 Ma B.P. This tectonic movement, which leads to uplift of the Qinghai_Xizang (Tibet) Plateau from 1 500 to 3 000-3 500 m, is periodic, abrupt and changeable in the movement rate of uplifting and slide slipping. 相似文献
187.
188.
A recording phase lag between ocean and continent climate changes: Constrained by the Matuyama/Brunhes polarity boundary 总被引:6,自引:0,他引:6
The Matuyama/Brunhes polarity boundary (MBPB) is recorded in Chinese loess L8, which is associated with the glacial period.
It is proved that loess L8 is capable of recording earth’s secular variation, and the lock-in depth in Chinese loess is no
more than that of marine sediments. Comparison with the location of MBPB in Chinese loess and marine sediments, it is put
forward that there is a recording phase lag between ocean and continent climate changes. 相似文献
189.
The development of stamen is an important stage during the sexual reproduction in higher plants. Studying the genes that predominantly
or even specifically expressed in stamens will aid in undestanding the molecular mechanism of stamen development. The structure
of a rice CHS-like gene (D5) which predominantly expressed in anthers has been analysised, showing high structural similarity
with two other anther-specific genes (A1 and BA42) fromBrassica napus. Northern analysis also reveals that the three genes share a similar expression pattern and that the expression of D5 may
relate to the early development of pollens. It is concluded that D5, A1 and BA42 represent a group of diverged CHS-like genes
which are related to stamen development. 相似文献
190.
The smectite to illite transformation in active geothermal systems of New Zealand can be simulated by a first-order reaction
kinetic model, which provides direct estimates about the minumum ages of active geothermal systems themselves. The derived
kinetic values show that the smectite to illite transformation is sensitive to both temperature and time. 相似文献