全文获取类型
收费全文 | 576253篇 |
免费 | 6542篇 |
国内免费 | 2224篇 |
专业分类
电工技术 | 9948篇 |
综合类 | 2703篇 |
化学工业 | 86104篇 |
金属工艺 | 25630篇 |
机械仪表 | 17486篇 |
建筑科学 | 14334篇 |
矿业工程 | 2802篇 |
能源动力 | 13248篇 |
轻工业 | 49042篇 |
水利工程 | 5919篇 |
石油天然气 | 8602篇 |
武器工业 | 19篇 |
无线电 | 66767篇 |
一般工业技术 | 109772篇 |
冶金工业 | 98865篇 |
原子能技术 | 10861篇 |
自动化技术 | 62917篇 |
出版年
2021年 | 3436篇 |
2019年 | 3208篇 |
2018年 | 19375篇 |
2017年 | 18246篇 |
2016年 | 15527篇 |
2015年 | 4697篇 |
2014年 | 7154篇 |
2013年 | 21626篇 |
2012年 | 14398篇 |
2011年 | 24739篇 |
2010年 | 20638篇 |
2009年 | 19778篇 |
2008年 | 21691篇 |
2007年 | 22596篇 |
2006年 | 13905篇 |
2005年 | 13899篇 |
2004年 | 13123篇 |
2003年 | 12979篇 |
2002年 | 12428篇 |
2001年 | 11988篇 |
2000年 | 11254篇 |
1999年 | 11808篇 |
1998年 | 29494篇 |
1997年 | 21266篇 |
1996年 | 16456篇 |
1995年 | 12368篇 |
1994年 | 11006篇 |
1993年 | 10816篇 |
1992年 | 7963篇 |
1991年 | 7920篇 |
1990年 | 7348篇 |
1989年 | 7297篇 |
1988年 | 7197篇 |
1987年 | 6112篇 |
1986年 | 6067篇 |
1985年 | 7083篇 |
1984年 | 6583篇 |
1983年 | 6025篇 |
1982年 | 5618篇 |
1981年 | 5768篇 |
1980年 | 5541篇 |
1979年 | 5304篇 |
1978年 | 5373篇 |
1977年 | 6374篇 |
1976年 | 8749篇 |
1975年 | 4791篇 |
1974年 | 4571篇 |
1973年 | 4586篇 |
1972年 | 3913篇 |
1971年 | 3600篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
121.
M Kanazawa M Yano C Namchai S Yamamoto A Ohtake M Takayanagi M Mori H Niimi 《Canadian Metallurgical Quarterly》1997,239(2):580-584
cDNAs for green fluorescent protein (GFP) and for a GFP fusion protein containing the presequence of human ornithine transcarbamylase (pOTC-GFP) were transfected into cultured human fibroblasts. GFP cDNA gave diffuse fluorescence throughout the cytoplasm and the nucleus, whereas pOTC-GFP cDNA gave mitochondria-associated fluorescence. Fluorescent mitochondrial structures could be classified into five patterns: thread-like mitochondria, fine thread-like ones, rod-like ones, granular ones, and granular ones with weak cytosolic fluorescence. pOTC-GFP mutants resulted in a loss of mitochondrial fluorescence and an appearance of weak fluorescence throughout the cytoplasm. pOTC-GFP cDNA was transfected into fibroblasts from patients with various mitochondrial diseases. Higher ratios of fibroblasts with granular mitochondria and those with fine thread-like ones were observed in a patient with Reye's syndrome and a patient with Kearns-Sayre syndrome. Weak cytosolic fluorescence was sometimes observed in fibroblasts from these patients. This method will be useful to analyze mitochondrial structural alterations and disorders of mitochondrial protein import. 相似文献
122.
123.
ME Sutherlin I Nishimori T Caffrey EP Bennett H Hassan U Mandel D Mack T Iwamura H Clausen MA Hollingsworth 《Canadian Metallurgical Quarterly》1997,57(21):4744-4748
The levels of mRNA expression of three UDP-N-acetyl-alpha-D-galactosamine:polypeptide GalNAc N-acetylgalactosaminyltransferases (GalNAc-transferases) were quantified for human adenocarcinoma cell lines from pancreas, colon, stomach, and breast. Two of the GalNAc-transferases, GalNAc-T1 and GalNAc-T2, were expressed constitutively and at low levels in most or all cell lines examined. A third GalNAc-transferase, GalNAc-T3, was differentially expressed. Well-differentiated adenocarcinoma cell lines expressed high levels and moderately differentiated cell lines expressed lower levels of GalNAc-T3. Cell lines classified as poorly differentiated failed to express GalNAc-T3 mRNA at levels that could be detected by Northern blot analysis. Differential expression of the GalNAc-T3 protein was confirmed in these cell lines by Western blotting. We propose that glycosylation in tumor cell lines may be regulated in part by differential expression of GalNAc-transferases, and we suggest that GalNAc-T3 gene expression may be a molecular indicator of differentiated adenocarcinoma. 相似文献
124.
P Virsik-Peuckert M Rave-Fr?nk U Langebrake H Schmidberger 《Canadian Metallurgical Quarterly》1997,148(3):209-215
The modulatory role of locally produced cyclooxygenase products and endothelium-derived nitric oxide in controlling vascular tone was investigated in bovine intra-mammary artery. Vascular reactivity initiated by vasoactive compounds, endothelin-1 (ET-1), bradykinin (BK), and substance P (SP) was measured isometrically in an isolated tissue bath. The effects of a cyclooxygenase inhibitor, indomethacin (10(-5) M) and an inhibitor of nitric oxide production, N omega-Nitro L-Arginine (L-NNA: 3 x 10(-4) M) were determined during agonist-mediated responses. Indomethacin alone markedly enhanced vascular contraction produced by ET-1, while L-NNA did not. Inhibition of endothelium-derived nitric oxide synthesis by L-NNA, however, significantly attenuated BK- and SP-induced vascular relaxations, whereas indomethacin had slight influence. The potentiation between indomethacin and L-NNA in regulating vasomotor tone was not observed in this vascular bed. Thus, it appeared that both the cyclooxygenase and endothelium-derived nitric oxide pathways participated in modifying vascular reactivity. Domination of one pathway over the other depended upon the agonist used to stimulate vascular tissue. 相似文献
125.
A new commercially available diode model is described. This unified model is capable of simulating the widest range of diode technologies of any presently available. The emphasis of this paper is on describing the model's extensive features and flexibility in the different domains of operation and is of particular interest in power applications 相似文献
126.
In order to observe the transport ability of peritoneum to small molecular substances, peritoneal equilibration test (PET) was performed in 52 CAPD patients. By analysing the relationship between peritoneal transport function and dialysis adequacy, we found the average urea KT/V and Cr were significantly lower in high and low transport groups (n = 6 and n = 2) than in high average and low average groups (n = 35 and n = 9). According to the results of PET, we adjusted the dialysis program of 11 patients and the dialysis adequacy was markedly improved. We concluded that PET was helpful for selecting and adjusting CAPD program, and discussed some questions which should be payed more attention in PET operation. 相似文献
127.
For part I see, ibid., p. 134, 1998. The basic approach outlined in the previous article is applied to the difficult problem of computing the optical modes of a vertical-cavity surface-emitting laser. The formulation utilizes a finite difference equation based upon the lowest order term of an infinite series solution of the scalar Helmholtz equation in a local region. This difference equation becomes exact in the one-dimensional (1-D) limit, and is thus ideally suited for nearly 1-D devices such as vertical-cavity lasers. The performance of the resulting code is tested on both a simple cylindrical cavity with known solutions and an oxide-confined vertical-cavity laser structure, and the results compared against second-order-accurate code based upon Crank-Nicolson differencing 相似文献
128.
John C. Hart Gordon W. Lescinsky Daniel J. Sandin Thomas A. DeFanti Louis H. Kauffman 《The Visual computer》1993,9(7):346-355
The pipelined architecture and parallel organization of the AT&T Pixel Machine image computer are described and demonstrated with applications for the visualization of multidimensional fractals, particularly linear fractals and quaternion/ stacked Julia sets. Techniques for pushing the Pixel Machine to its peak abilities are described and apply to more recent parallel image computers as well. 相似文献
129.
Jan van Eijck 《Formal Aspects of Computing》1994,6(1):766-787
Presuppositions of utterances are the pieces of information you convey with an utterance no matter whether your utterance is true or not. We first study presupposition in a very simple framework of updating propositional information, with examples of how presuppositions of complex propositional updates can be calculated. Next we move on to presuppositions and quantification, in the context of a dynamic version of predicate logic, suitably modified to allow for presupposition failure. In both the propositional and the quantificational case, presupposition failure can be viewed as error abortion of procedures. Thus, a dynamic assertion logic which describes the preconditions for error abortion is the suitable tool for analysing presupposition. 相似文献
130.