全文获取类型
收费全文 | 20511篇 |
免费 | 1452篇 |
国内免费 | 793篇 |
专业分类
电工技术 | 1011篇 |
技术理论 | 4篇 |
综合类 | 1022篇 |
化学工业 | 3598篇 |
金属工艺 | 881篇 |
机械仪表 | 1176篇 |
建筑科学 | 1327篇 |
矿业工程 | 521篇 |
能源动力 | 551篇 |
轻工业 | 1075篇 |
水利工程 | 289篇 |
石油天然气 | 1119篇 |
武器工业 | 127篇 |
无线电 | 2612篇 |
一般工业技术 | 2623篇 |
冶金工业 | 1837篇 |
原子能技术 | 166篇 |
自动化技术 | 2817篇 |
出版年
2024年 | 62篇 |
2023年 | 308篇 |
2022年 | 520篇 |
2021年 | 747篇 |
2020年 | 548篇 |
2019年 | 509篇 |
2018年 | 568篇 |
2017年 | 587篇 |
2016年 | 548篇 |
2015年 | 681篇 |
2014年 | 891篇 |
2013年 | 1210篇 |
2012年 | 1131篇 |
2011年 | 1274篇 |
2010年 | 990篇 |
2009年 | 1024篇 |
2008年 | 1004篇 |
2007年 | 964篇 |
2006年 | 1015篇 |
2005年 | 914篇 |
2004年 | 610篇 |
2003年 | 597篇 |
2002年 | 519篇 |
2001年 | 442篇 |
2000年 | 525篇 |
1999年 | 607篇 |
1998年 | 787篇 |
1997年 | 589篇 |
1996年 | 524篇 |
1995年 | 370篇 |
1994年 | 356篇 |
1993年 | 264篇 |
1992年 | 173篇 |
1991年 | 145篇 |
1990年 | 129篇 |
1989年 | 100篇 |
1988年 | 83篇 |
1987年 | 61篇 |
1986年 | 53篇 |
1985年 | 41篇 |
1984年 | 21篇 |
1983年 | 18篇 |
1982年 | 33篇 |
1981年 | 24篇 |
1980年 | 25篇 |
1979年 | 10篇 |
1978年 | 12篇 |
1977年 | 35篇 |
1976年 | 73篇 |
1971年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
EH Eddes AM Masclee HG Gooszen M Fr?lich CB Lamers 《Canadian Metallurgical Quarterly》1997,174(4):387-392
Two mobilizable cloning vectors, designated pABW1 and pAWB2, were constructed basing on the E. coli vector pBGS18 and oriT originating from RK2. In pABW2 the kanamycin resistance gene was replaced by a novel tetracycline resistance cassette derived from Tn1721. Both vectors, specific for E. coli, allow to perform the cloning steps in E. coli and then to efficiently transfer the constructs by conjugation to the host of choice. A vector which cannot propagate in the given host can be applied for identification of the host specific plasmid replicator regions. With the use of pABW2 we defined the minimal replicator region of pTAV202-a mini-derivative of the large pTAV1 plasmid of P. versutus. We also proved that RepC' encoded on this fragment is the principal initiator replication protein and that oriV is located along its coding sequence. 相似文献
52.
Ten groups of 14 immunosuppressed NMRI-mice (nu/nu) were raised and kept under germ-reduced conditions. The control animals were fed a germ-reduced diet, nine other groups received the same diet with selegiline (CAS 14611-51-9, Deprenyl) or lipoic acid (thioctic acid, CAS 62-46-4) admixed at various amounts. The 50% survival rate, the total life span of each group and the areas under the curves were determined to evaluate life expectancy as compared to the controls. The racemate of lipoic acid at high dosage (350 mg/kg body weight) reduced the life span significantly. The S(-)-enantiomer of lipoic acid (75 mg/kg body weight) increased the 50% survival rate, whereas the physiologic R(+)-enantiomer (9 mg/kg body weight) expanded the total life span of its group. Alteration of only one out of three parameters was not considered significant. All other groups except for one did not differ from controls: only animals which obtained 75 micrograms selegiline per kg of body weight and per day exerted increased life expectancies by all three parameters. This group exhibited also in statistical evaluation a significantly (p < 0.05) prolongated survival time up to about 200% as compared to the control animals. 相似文献
53.
一个矢量形式的双圆弧插值算法 总被引:3,自引:1,他引:2
本文在分析数控插补最常用的双圆弧插值算法特点的基础上,将以局部坐标系中的三角运算为核心的传统双圆弧插值算法,改造成为以整体坐标系中的线性运算为核心的矢量形式的双圆弧插值算法,从而减少了计算的复杂性和程序的复杂性,提高了效率和可靠性。 相似文献
54.
结合实时法全息干涉计量和数字图象处理技术,提出了一种溶液扩散系数的自动测量系统。在干涉图的处理中,采用了相位检测和曲线拟合技术,得到了亚象素的测量精度。 相似文献
55.
重馏分油加氢脱氮反应动力学模型的研究 总被引:10,自引:1,他引:9
简要地介绍了一些典型的模型氮化物的HDN反应规律。根据胜利VGO在3722B催化剂上的大量HDN实验数据,提出了如下的HDN基本反应动力学方程:dCNdt=-k1+K*CNCNPH2为了扩大上式的应用范围,详细分析了各种因素(如原料油种类和馏程及H2S等)对HDN的影响,并开发了相应的经验关联式,从而得到了一个较完整的馏分油HDN反应动力学模型。验证实验表明,该模型是成功的。 相似文献
56.
57.
EH Sterck 《Canadian Metallurgical Quarterly》1997,42(3):179-198
Female dispersal occurs in a number of primate species. It may be related to: avoidance of inbreeding, reduction in food competition, reduction of predation risk, or avoidance of infanticide in combination with mate choice. Female dispersal was studied for a 5-year period in a wild population of Thomas langurs (Presbytis thomasi) that lived in one-male multi-female groups. Juvenile and adult individuals of both sexes were seen to disperse. Females appeared to transfer unhindered between groups, mostly from a larger group to a recently formed smaller one. They transferred without their infants and when not pregnant, and seemed to transfer preferentially during periods when extra-group males were harassing their group. During these inter-group encounters extra-group males seemed to try to commit infanticide. Thus, the timing of female transfer was probably closely linked to infanticide avoidance. Moreover, females seemed to transfer when the resident male of their group was no longer a good protector. The observations in the present study suggest that females transferred to reduce the risk of infanticide. Female dispersal may have another ultimate advantage as well, namely inbreeding avoidance. Due to the dispersal of both females and males the social organization of Thomas langurs was rather fluid. New groups were formed when females joined a male; male takeovers were not observed. Bisexual groups had only a limited life span, because all adult females of a bisexual group could emigrate. This pattern of unhindered female dispersal affects male reproductive strategies, and in particular it might lead to infanticidal behavior during inter-group encounters. 相似文献
58.
DL Lacey JM Erdmann SL Teitelbaum HL Tan J Ohara A Shioi 《Canadian Metallurgical Quarterly》1995,136(6):2367-2376
Interleukin 4 (IL-4) is an immune cytokine that inhibits bone resorption in mice and suppresses osteoclastic cell formation in vitro through an undefined mechanism. In this report, we have established the cellular identity of the IL-4 target cell using a variety of bone marrow/stromal cell coculture methods. Initially, we found that the majority of IL-4's inhibition of osteoclastic cell formation was due to its effect on bone marrow cells, not stromal cells. Consequently, bone marrow macrophages were used as osteoclastic cell progenitors after they had been transiently exposed to IL-4 (48 h), before the addition of stromal cells, 1,25-dihydroxyvitamin D3, and dexamethasone. In this circumstance, IL-4 impaired subsequent osteoclastic cell formation, suggesting that the macrophage may be potentially targeted by many factors known to influence osteoclast formation. Consequently, we discovered that interferon-gamma (IFN gamma), prostaglandin E (PGE), and cell-permeant cAMP analogs also impacted osteoclastic cell formation when used to selectively treat bone marrow macrophages. IFN gamma suppressed osteoclastic cell formation, whereas PGE and cAMP analog treatment led to the formation of significantly enlarged osteoclastic cells. Importantly, PGE antagonized the inhibitory effects of both IL-4 and IFN gamma on the osteoclastic cell-forming potential of bone marrow macrophages. Collectively, these findings establish bone marrow macrophages as osteoclastic cell precursors with the degree of their commitment to the osteoclast pathway sensitive to the effects of soluble mediators, including IL-4, IFN gamma, and PGE. 相似文献
59.
60.
Surface expression of the T cell antigen receptor (TCR) in mature T cells requires the association of a variable heterodimer (alpha.beta or gamma.delta) with six invariant CD3 polypeptides (gamma, delta, epsilon-epsilon, zeta-zeta, or zeta-eta). We described here that deletion of the cytoplasmic tail polypeptide sequence (Lys-Lys-Lys-Asn-Ser) of TCR beta-chain (beta CT) results in expression of the truncated beta-chain on the surface of a mature T cell hybridoma line, in the absence of TCR-alpha, as a glycophosphatidylinositol (GPI)-anchored monomeric polypeptide. The GPI-anchored TCR-beta CT is not associated with CD3-epsilon and is incapable of conventional signal transduction. Association with TCR-alpha prevents beta CT from GPI-linkage formation. The alpha beta CT heterodimer binds the CD3 polypeptides, and the resultant TCR alpha beta CT/CD3 complex is capable of signal transduction. Our data show that a signal sequence for GPI-linkage formation is present in TCR-beta, and this alternative membrane anchoring mechanism can be utilized by beta-chain polypeptide lacking the CT sequence. We conclude therefore that in the absence of TCR-alpha expression, the beta-chain CT sequence plays an essential function in hindering GPI-linkage formation, thereby preventing escape of incompletely assembled TCR beta-chain to the cell surface of mature T cells. 相似文献