全文获取类型
收费全文 | 11727篇 |
免费 | 44篇 |
国内免费 | 72篇 |
专业分类
系统科学 | 62篇 |
丛书文集 | 29篇 |
教育与普及 | 21篇 |
理论与方法论 | 32篇 |
现状及发展 | 5449篇 |
研究方法 | 601篇 |
综合类 | 5521篇 |
自然研究 | 128篇 |
出版年
2012年 | 208篇 |
2011年 | 311篇 |
2010年 | 78篇 |
2009年 | 75篇 |
2008年 | 206篇 |
2007年 | 250篇 |
2006年 | 254篇 |
2005年 | 240篇 |
2004年 | 206篇 |
2003年 | 198篇 |
2002年 | 252篇 |
2001年 | 438篇 |
2000年 | 432篇 |
1999年 | 288篇 |
1992年 | 241篇 |
1991年 | 196篇 |
1990年 | 216篇 |
1989年 | 191篇 |
1988年 | 202篇 |
1987年 | 220篇 |
1986年 | 190篇 |
1985年 | 253篇 |
1984年 | 229篇 |
1983年 | 172篇 |
1982年 | 177篇 |
1981年 | 181篇 |
1980年 | 170篇 |
1979年 | 403篇 |
1978年 | 342篇 |
1977年 | 252篇 |
1976年 | 291篇 |
1975年 | 262篇 |
1974年 | 272篇 |
1973年 | 224篇 |
1972年 | 246篇 |
1971年 | 308篇 |
1970年 | 375篇 |
1969年 | 256篇 |
1968年 | 307篇 |
1967年 | 295篇 |
1966年 | 249篇 |
1965年 | 178篇 |
1964年 | 99篇 |
1959年 | 88篇 |
1958年 | 162篇 |
1957年 | 100篇 |
1956年 | 91篇 |
1955年 | 85篇 |
1954年 | 77篇 |
1948年 | 64篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
911.
K.G. Subramanian R. Saravanan M. Geethalakshmi P. Helen Chandra M. Margenstern 《自然科学进展》2007,17(4):479-485
Array P systems were introduced by Paun Gh. which is linking the two areas of membrane computing and picture grammars. Puzzle grammars were introduced by us for generating connected picture arrays in the two-dimensional plane, motivated by the problem of tiling the plane. On the other hand, incorporating into arrays the developmental type of generation used in the well-known biologically motivated L systems, Siromoney and Siromoney proposed a very general rectangular array generating model, called extended controlled tabled L array system (ECTLAS). In this paper we introduce two variations of the array P system, called BPG array P system and parallel array P system. The former has in the regions array objects and basic puzzle grammar rules (BPG), which are a specific kind of puzzle grammar rules. In the latter, the regions have rectangular array objects and tables of context-free rules. We examine these two types of P systems for their array generative power. 相似文献
912.
本书的作者在大学讲授应用数学有30多年,在教学中发现,已有的一些教材并不完全适用,于是作者根据实际情况,逐步用自已的方式教学,最后编写了本书。虽然书中的内容并不是全新的,但表述的方式要比已有教材好,使大学生容易阅读,因此, 相似文献
913.
An experimental pectate lyase enzyme was used toscour knitted cotton fabric and the emphasis was on pectinremoval. Using an enzyme dosage of 0.2 g/L at temperature55℃ and pH 6.35 for 30 rain, good scouring properties wereobtained. When appropriate concentrations of 1 - HydroxyEthylidene- 1, 1 - Diphosphonic Acid(HEDP) and CaCl2were added, the percentage pectin removal improvedsignificantly. 相似文献
914.
ZHANG XianPing MA YanWei GAO ZhaoShun YU ZhengGuang WANG DongLiang WATANABE K GUO JianDong 《科学通报(英文版)》2007,52(18):2477-2480
Nano-SiC doped MgB2 tapes were prepared by the in situ powder-in-tube method. Heat treatment was performed at 650℃ for 1 h. XRD data indicate that SiC particles had reacted with the MgB2 during sintering process. MgB2 core seemed to be denser after SiC doping, and the critical temperature was slightly depressed. The critical current density Jc of the SiC doped tapes was significantly enhanced in magnetic fields up to 14 T compared to the undoped ones. For the 5% SiC doped samples, Jc was in- creased by a factor of 32 at 4.2 K, 10 T. The enhancement of Jc-B properties in SiC doped MgB2 tapes is considered to be due to the enhancement of grain linkages and the introduction of effective flux pining centers. The substitution of B by C in MgB2 grains is thought to be the main reason for the improve- ment of the flux pinning ability in SiC doped MgB2 tapes. 相似文献
915.
K J Mikolajczak R V Madrigal J K Rupprecht Y H Hui Y M Liu D L Smith J L McLaughlin 《Experientia》1990,46(3):324-327
Sylvaticin (I), a new tetrahydroxy annonaceous acetogenin with nonadjacent tetrahydrofuran rings, has been isolated from the dried fruits of Rollinia sylvatica St. Hil. (Annonaceae). This compound is extremely cytotoxic to human tumor cells and shows promising insect control properties. 相似文献
916.
917.
P. Milner V. Ralevic A. M. Hopwood E. Fehér J. Lincoln K. A. Kirkpatrick G. Burnstock 《Cellular and molecular life sciences : CMLS》1989,45(2):121-125
Substance P and choline acetyltransferase have been localised in a small proportion of endothelial cells of rat coronary arteries using electron microscopic immunocytochemistry. During a hypoxic period of 1 min, coronary vasodilatation was produced in the Langendorff heart preparation and increased levels of substance P and acetylcholine were released into the perfusate. The possibility that these substances are released from endothelial cells during hypoxia and contribute to the hyperaemic response is discussed. 相似文献
918.
The in situ activity of 3 beta-hydroxysteroid dehydrogenase was detected in clustered cells which showed steroid-producing morphology, within the capsule of the paraaortic lymph node. In light and electron microscopic studies, the positive reaction products were detected on intracapsular cell clusters. This result indicates that these unique cells may have a steroid secreting function within the lymph nodes. 相似文献
919.
Herbert K.H. Lee 《Journal of Classification》2007,24(1):53-70
Feedforward neural networks are a popular tool for classification, offering a method for fully flexible modeling. This paper
looks at the underlying probability model, so as to understand statistically what is going on in order to facilitate an intelligent
choice of prior for a fully Bayesian analysis. The parameters turn out to be difficult or impossible to interpret, and yet
a coherent prior requires a quantification of this inherent uncertainty. Several approaches are discussed, including flat
priors, Jeffreys priors and reference priors. 相似文献
920.
Construction of chimaeric processed immunoglobulin genes containing mouse variable and human constant region sequences 总被引:3,自引:0,他引:3
The specificity of monoclonal antibodies provides a powerful diagnostic and therapeutic tool in investigating human neoplasia. Radiological scanning and immunotherapy with mouse tumour-specific monoclonal antibodies have been applied to patients with some success, but a major problem is the neutralization of the mouse antibody induced by repeated administration of heterologous antibodies. To avoid or reduce such immune reactions, chimaeric immunoglobulins consisting of mouse variable (V) and human constant (C) regions can be synthesized. We have constructed a recombinant retrovirus DNA carrying genomic heavy-chain (H) variable-diversity joining (VH-D-JH) and C gamma 1 genes from different species and show here that the chimaeric intervening sequences are spliced out precisely. This procedure provides a useful method to construct the chimaeric mouse-human immunoglobulin gene to be expressed in Escherichia coli, yeast and animal cells. Unexpectedly, a hidden splice donor site in the 5'-flanking region of a human VH gene is used in place of the donor site of the leader sequence exon, resulting in the formation of the V region without the leader sequence. 相似文献