全文获取类型
收费全文 | 25538篇 |
免费 | 65篇 |
国内免费 | 83篇 |
专业分类
系统科学 | 104篇 |
丛书文集 | 184篇 |
教育与普及 | 59篇 |
理论与方法论 | 93篇 |
现状及发展 | 10100篇 |
研究方法 | 1095篇 |
综合类 | 13605篇 |
自然研究 | 446篇 |
出版年
2013年 | 240篇 |
2012年 | 361篇 |
2011年 | 804篇 |
2010年 | 172篇 |
2008年 | 402篇 |
2007年 | 491篇 |
2006年 | 469篇 |
2005年 | 464篇 |
2004年 | 456篇 |
2003年 | 443篇 |
2002年 | 433篇 |
2001年 | 915篇 |
2000年 | 906篇 |
1999年 | 549篇 |
1993年 | 106篇 |
1992年 | 536篇 |
1991年 | 441篇 |
1990年 | 457篇 |
1989年 | 455篇 |
1988年 | 453篇 |
1987年 | 424篇 |
1986年 | 407篇 |
1985年 | 492篇 |
1984年 | 405篇 |
1983年 | 352篇 |
1982年 | 333篇 |
1981年 | 288篇 |
1980年 | 350篇 |
1979年 | 809篇 |
1978年 | 618篇 |
1977年 | 589篇 |
1976年 | 499篇 |
1975年 | 573篇 |
1974年 | 742篇 |
1973年 | 641篇 |
1972年 | 675篇 |
1971年 | 776篇 |
1970年 | 948篇 |
1969年 | 714篇 |
1968年 | 766篇 |
1967年 | 689篇 |
1966年 | 661篇 |
1965年 | 435篇 |
1959年 | 218篇 |
1958年 | 405篇 |
1957年 | 277篇 |
1956年 | 227篇 |
1955年 | 206篇 |
1954年 | 181篇 |
1948年 | 163篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
871.
王建伦 《国外科技新书评介》2006,(2):5-6
本书是关于线性和非线性有限单元法的入门教材,是根据作者在过去12年里为美国新奥尔良大学的多个专业学生讲授这两门课程的基础上逐步编撰而成。本书不同于已有教材,有许多新颖的特点,如重视基础应用,力求最少涉及数学理论;内容涉及的专业范围宽,选用大量不同专业的问题进行引导,可供多种学科背景的学生学习;在讲述理论的同时将相关软件的使用贯穿全书。 相似文献
872.
本书全面论述了传输、管理和控制位面的技术,介绍了一些有用的、现行的和下一代电讯网络技术的参考信息。四位作者均在电信学研究、产品开发等方面具有20年以上的经验。 相似文献
873.
J C Chabala V B Waits T Ikeler A A Patchett L Payne L H Peterson R A Reamer K Hoogsteen M Wyvratt W L Hanson 《Experientia》1991,47(1):51-53
1-(Substituted)benzyl-5-aminoimidazole-4-carboxamides are potent orally active inhibitors of Trypanosoma cruzi infections in mice. The most active compounds are the 1-(4-chlorobenzyl)- and 1-(3,4-dichlorobenzyl)-analogs (L-153,094 [2] and L-153,153 [4], resp.) which are approximately 7-fold more potent upon oral administration than nifurtimox (Lampit) in suppressing parasite levels in the blood of mice with acute Trypanosoma cruzi infections. 相似文献
874.
Glucose/galactose malabsorption (GGM) is an autosomal recessive disease manifesting within the first weeks of life and characterized by a selective failure to absorb dietary glucose and galactose from the intestine. The consequent severe diarrhoea and dehydration are usually fatal unless these sugars are eliminated from the diet. Intestinal biopsies of GGM patients have revealed a specific defect in Na(+)-dependent absorption of glucose in the brush border. Normal glucose absorption is mediated by the Na+/glucose cotransporter in the brush border membrane of the intestinal epithelium. Cellular influx is driven by the transmembrane Na+ electrochemical potential gradient; thereafter the sugar moves to the blood across the basolateral membrane via the facilitated glucose carrier. We have previously cloned and sequenced a Na+/glucose cotransporter from normal human ileum and shown that this gene, SGLT1, resides on the distal q arm of chromosome 22. We have now amplified SGLT1 complementary DNA and genomic DNA from members of a family affected with GGM by the polymerase chain reaction. Sequence analysis of the amplified products has revealed a single missense mutation in SGLT1 which cosegregates with the GGM phenotype and results in a complete loss of Na(+)-dependent glucose transport in Xenopus oocytes injected with this complementary RNA. 相似文献
875.
党刚 《国外科技新书评介》2006,(2):20-21
这是一本关于哲学如何给物理带来灵感,而物理又如何去影响哲学的书。哲学给科学带来基本观念和预设,但通过科学发现,这些观念又常常受到怀疑和修正,而伟大的科学家常常知道这种影响的脉络所在。本书通过清晰的论述和精美的插图,以科学哲人为中心讲述了他们的伟大发现,以及什么力量又促使他们重新考虑那些过去科学描述自然世界的惯常观念。书中还阐述了:因为电磁学、热力学和原子结构上的发现,使我们对科学和自然的理解经历了基本概念上的改变。 相似文献
876.
877.
D. DiFrancesco F. Porciatti I. S. Cohen 《Cellular and molecular life sciences : CMLS》1991,47(5):449-452
Summary The isolation of ionic fluxes contributing to electric currents through cell membranes often requires block of other undesired components which can be achieved, among others, by divalent cations. Mn2+ and Ba2+ are often used, for example, to block Ca and K currents. Here we have investigated the effects of these two cations on the properties of the hyperpolarization-activated pacemaker current if, in rabbit sino-atrial node myocytes, as obtained by voltage clamp analysis. We find that 2 mM Mn2+ shifts the if activation curve by 3.2±0.3 mV towards more positive values. However, when 1 mM Ba2+ is also added, the positive shift is more than halved (1.3±0.2 mV). We find, too, that in the absence of blocking cations the ACh-induced if inhibition is slightly higher than in their presence. These results indicate that the alteration of if kinetic properties by Ba2+ plus Mn2+-containing solutions is minimal. 相似文献
878.
Mulhern S. A. Stroube W. B. Jacobs R. M. 《Cellular and molecular life sciences : CMLS》1986,42(5):551-553
Summary Second generation mice were exposed to normal (50 ppm, Group I) or excess (2000 ppm, Group II) zinc in the maternal diet during gestation and lactation, then weaned and continued on the mother's diet until sacrifice at 8 weeks. Tibia zinc reflected dietary intake. Group II had reduced plasma copper, body weight, and hematocrit; the second coat of hair appeared late and was lighter in color than Group I, possibly as an effect of copper and pigmentation development and hair growth. 相似文献
879.
880.
Cells with electron-dense secretory vesicles use them to store only specialized secretory products such as peptide hormones; other types of secreted proteins are externalized by an alternative, constitutive route. One possible mechanism for such segregation is that proteins destined for dense secretory vesicles contain unique 'sorting domains' that allow for selective targeting. Here, we set out to determine whether a constitutively secreted protein could be diverted to the dense secretory vesicles by attachment to a peptide hormone sequence. We made use of the ability of the mouse pituitary tumour cell, AtT-20, to correctly sort exogenous secretory proteins introduced into them by DNA transfection. We constructed a plasmid encoding a hybrid protein in which a constitutively secreted viral protein was fused to the carboxy terminus of human growth hormone (hGH). Cells expressing the hybrid protein were found to target it to dense secretory vesicles with an efficiency close to that observed for the parental hGH. These results support the hypothesis that sorting domains on peptide hormones direct their packaging into dense secretory vesicles. The results also suggest that proteins secreted by the constitutive pathway either do not contain any sorting domain, or their sorting signals can be overridden by those which direct peptide hormones. 相似文献