全文获取类型
收费全文 | 43402篇 |
免费 | 223篇 |
国内免费 | 478篇 |
专业分类
系统科学 | 576篇 |
丛书文集 | 865篇 |
教育与普及 | 116篇 |
理论与方法论 | 170篇 |
现状及发展 | 18002篇 |
研究方法 | 1603篇 |
综合类 | 21922篇 |
自然研究 | 849篇 |
出版年
2014年 | 273篇 |
2013年 | 564篇 |
2012年 | 810篇 |
2011年 | 1668篇 |
2010年 | 528篇 |
2009年 | 474篇 |
2008年 | 951篇 |
2007年 | 1110篇 |
2006年 | 1104篇 |
2005年 | 1000篇 |
2004年 | 890篇 |
2003年 | 860篇 |
2002年 | 999篇 |
2001年 | 1408篇 |
2000年 | 1332篇 |
1999年 | 914篇 |
1992年 | 766篇 |
1991年 | 587篇 |
1990年 | 629篇 |
1989年 | 609篇 |
1988年 | 590篇 |
1987年 | 674篇 |
1986年 | 606篇 |
1985年 | 751篇 |
1984年 | 618篇 |
1983年 | 469篇 |
1982年 | 462篇 |
1981年 | 481篇 |
1980年 | 592篇 |
1979年 | 1204篇 |
1978年 | 982篇 |
1977年 | 990篇 |
1976年 | 812篇 |
1975年 | 862篇 |
1974年 | 1186篇 |
1973年 | 1030篇 |
1972年 | 1039篇 |
1971年 | 1152篇 |
1970年 | 1448篇 |
1969年 | 1140篇 |
1968年 | 1124篇 |
1967年 | 1133篇 |
1966年 | 976篇 |
1965年 | 711篇 |
1959年 | 383篇 |
1958年 | 636篇 |
1957年 | 441篇 |
1956年 | 374篇 |
1955年 | 366篇 |
1954年 | 352篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
The rough endoplasmic reticulum membranes of mammalian cells contain specific ribosome-binding sites. A purification to apparent homogeneity of a negatively charged protein (ERp180) of relative molecular mass 180,000 (180 K) was reported which was proposed to function as a rough endoplasmic reticulum ribosome receptor. We report here that ribosome-binding site activity quantitatively solubilized from rough endoplasmic reticulum membranes does not cofractionate with ERp180. By contrast, ribosome-binding site activity fractionates as a much smaller, positively charged protein. 相似文献
82.
Genotoxic effects of dithane M-45 were studied on the bone marrow cells of male albino mice (Lacca strain) in vivo. Different doses (30 mg, 40 mg and 300 mg/kg b.wt) of dithane M-45 were injected intraperitoneally and their effects were investigated after time intervals of 1, 2, 5 and 10 days. The chromosomal aberrations observed in the bone marrow cells of male mice after treatment with dithane M-45 were fragments, rings, dicentric chromosomes, terminal chromatid deletions, chromatid gaps and breaks. In addition to these chromosomal aberrations, physiological effects such as uneven stretching of chromatin material, end-to-end chromosomal associations, exchange configurations, clumping, stickiness and centromeric associations were also observed. 相似文献
83.
84.
Tad M. Schmaltz 《Studies in history and philosophy of science》2003,34(4):737-762
There is considerable debate among scholars over whether Descartes allowed for genuine body–body interaction. I begin by considering Michael Della Rocca’s recent claim that Descartes accepted such interaction, and that his doctrine of the creation of the eternal truths indicates how this interaction could be acceptable to him. Though I agree that Descartes was inclined to accept real bodily causes of motion, I differ from Della Rocca in emphasizing that his ontology ultimately does not allow for them. This is not the end of the story however, since two of Descartes’s successors offered incompatible ways of developing his conflicted account of motion. I contrast the occasionalist view of Nicolas Malebranche that changes in motion derive directly from divine volitions with the non-occasionalist claim of Pierre-Sylvain Regis that such changes derive from a nature distinct from God. In light of Della Rocca’s interpretation, it is noteworthy that the issue of eternal truths is relevant to both alternative accounts. Indeed, Regis took the doctrine that such truths are created to provide crucial support for his alternative to an occasionalist account of body–body interaction. What does not help Della Rocca, however, is that Regis’s view of motion requires a fundamental revision of Descartes’s ontology. 相似文献
85.
秋水仙素诱导青虾次级卵母细胞二倍体初探 总被引:3,自引:0,他引:3
以青虾卵巢为材料,采用秋水仙素诱导多倍体次级卵母细胞.经滴片试验,确立此实验最佳滴片高度为1.5cm,通过设置5个秋水仙素浓度(0.08~0.40mg/mL)及3个作用时间(6~24h),观察发生染色体加倍的细胞相对数目.实验结果表明:在使用秋水仙素的浓度为0.08~0.40mg/mL,处理6~24h时都可以获得多倍体卵细胞.在秋水仙素浓度是0.32mg/mL,处理6h可得到最高二倍体突变率(32.58%).还测试了0.32mg/mL COM作用6h时ATPase活性与生理盐水对照组的变化,结果显示COM会在一定程度上影响细胞的新陈代谢.但是50%左右的成活率表明,这种诱导突变的方法仍具有一定的应用价值. 相似文献
86.
易中天教授在《品三国》中,把历史唯物主义具体化,提出了评论历史人物和历史事件的三项准则,即:“还原”、“比较”、“分析”。易教授在贯彻这三项原则时也难免有疏漏之处:一、把襄阳、赤壁之战说成曹刘之战不能成立;二、曹操一封信促成孙刘联盟的提法不妥;三、《白衣渡江》引用了《吕蒙传》上有两条错误的史料。 相似文献
87.
88.
89.
针对ADO.NET在处理"丢失的修改"问题时,不支持"关键字和已修改字段"的并发控制问题提出了相应的解决办法;同时对ADO.NET架构本身带来的异常更新问题提供了解决思路. 相似文献