全文获取类型
收费全文 | 3665篇 |
免费 | 8篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 11篇 |
化学工业 | 69篇 |
金属工艺 | 18篇 |
机械仪表 | 14篇 |
建筑科学 | 19篇 |
矿业工程 | 1篇 |
能源动力 | 10篇 |
轻工业 | 80篇 |
水利工程 | 3篇 |
石油天然气 | 2篇 |
无线电 | 147篇 |
一般工业技术 | 75篇 |
冶金工业 | 3105篇 |
原子能技术 | 3篇 |
自动化技术 | 119篇 |
出版年
2022年 | 5篇 |
2016年 | 6篇 |
2015年 | 14篇 |
2014年 | 7篇 |
2013年 | 27篇 |
2012年 | 17篇 |
2011年 | 27篇 |
2010年 | 16篇 |
2009年 | 29篇 |
2008年 | 28篇 |
2007年 | 36篇 |
2006年 | 33篇 |
2005年 | 27篇 |
2004年 | 31篇 |
2003年 | 23篇 |
2002年 | 25篇 |
2001年 | 18篇 |
2000年 | 26篇 |
1999年 | 85篇 |
1998年 | 936篇 |
1997年 | 558篇 |
1996年 | 348篇 |
1995年 | 233篇 |
1994年 | 141篇 |
1993年 | 182篇 |
1992年 | 34篇 |
1991年 | 30篇 |
1990年 | 43篇 |
1989年 | 27篇 |
1988年 | 42篇 |
1987年 | 39篇 |
1986年 | 27篇 |
1985年 | 34篇 |
1984年 | 10篇 |
1983年 | 19篇 |
1982年 | 23篇 |
1981年 | 39篇 |
1980年 | 25篇 |
1979年 | 5篇 |
1978年 | 18篇 |
1977年 | 105篇 |
1976年 | 192篇 |
1975年 | 12篇 |
1974年 | 7篇 |
1973年 | 12篇 |
1972年 | 6篇 |
1971年 | 4篇 |
1969年 | 5篇 |
1961年 | 4篇 |
1955年 | 4篇 |
排序方式: 共有3676条查询结果,搜索用时 22 毫秒
121.
Oral fibroblasts stimulated invasion of oral-carcinoma cells into the collagen matrix. The mechanisms of the fibroblast-induced stimulation of invasiveness was further investigated by examining cell motility and proteolytic activity of tumor cells, using mainly an adenoid-cystic-carcinoma cell line (ACCS) and normal fibroblasts from gingival tissues. Conditioned medium from the fibroblasts grown in serum-free medium was fractionated on a Superdex 200 pg column, and Peak 1 eluted at 200 to 300 kDa and Peak 2 eluted at 50 to 100 kDa were found to contain different specific activity. Treatment of ACCS cells with Peak 1 resulted in an increase in the production of proteolytic enzymes. Peak 2 stimulated both chemotaxis and chemokinesis of ACCS cells. A chemotactic factor was purified from the heparin-unbound fraction of Peak 2 by anion exchange and hydrophobic chromatography, and was named "fibroblast-derived motility factor (FDMF)". At 1 microg/ml, FDMF stimulated chemotaxis of ACCS cells by 4-fold compared with unstimulated controls. Characterization of the physicochemical properties of FDMF suggested that it might be different from any known motility factors. Exposure of ACCS cells to FDMF resulted in reduced amounts of actin stress fiber in the cytoplasm and induction of tyrosine phosphorylation of several cellular proteins detectable 30 to 60 min after treatment. These FDMF-induced changes were blocked by pre-treatment either with genistein or with pertussis toxin. These findings suggest that FDMF may be a novel protein which stimulates cell motility via a signaling pathway mediated by a pertussis-toxin-sensitive G protein and tyrosine phosphorylation. 相似文献
122.
Perinuclear antineutrophil cytoplasmic antibodies in patients with Crohn's disease define a clinical subgroup 总被引:1,自引:0,他引:1
EA Vasiliauskas SE Plevy CJ Landers SW Binder DM Ferguson H Yang JI Rotter A Vidrich SR Targan 《Canadian Metallurgical Quarterly》1996,110(6):1810-1819
BACKGROUND & AIMS: Antineutrophil cytoplasmic antibodies (ANCA) have been consistently detected in a subgroup of patients with Crohn's disease (CD). This study was designed to determine whether serum ANCA expression in patients with CD characterizes an identifiable clinical subgroup. METHODS: The study population consisted of 69 consecutive patients with an established diagnosis of CD as determined by a combination of characteristic clinical, radiographic, endoscopic, and histopathologic criteria. Sera from the patients were analyzed for the presence of ANCAs using the fixed neutrophil enzyme-linked immunosorbent assay (ELISA) assay. Perinuclear ANCA (pANCA)-positive and cytoplasmic ANCA (cANCA)-positive results by ELISA were confirmed by indirect immunofluorescence staining. Clinical profiles of the ANCA-positive patients with CD were compared with those of patients with CD not expressing ANCA (ANCA-negative). RESULTS: pANCA-positive patients with CD have endoscopically and/or histopathologically documented left-sided colitis and symptoms of left-sided colonic inflammation, clinically reflected by rectal bleeding and mucus discharge, urgency, and treatment with topical agents. One hundred percent of patients with CD expressing pANCA had "UC-like" features. CONCLUSIONS: In patients with CD, serum pANCA expression characterizes a UC-like clinical phenotype. Stratification of CD by serum pANCA provides evidence of heterogeneity within CD and suggests a common intestinal mucosal inflammatory process among a definable subgroup of patients with CD and UC expressing this marker. 相似文献
123.
124.
IR Sanderson AJ Ouellette EA Carter PR Harmatz 《Canadian Metallurgical Quarterly》1993,105(4):974-980
BACKGROUND: Exogenous antigenic peptides are presented to T cells by class II major histocompatibility complex (Ia) molecules on the surface of antigen-presenting cells. Class II-associated invariant chain (Ii) is also required for effective antigen presentation. Because messenger RNAs (mRNAs) for Ii chain and for class II I-A beta chain appear in the mouse intestinal epithelium after weaning, experiments were conducted to test the effect of age of weaning and diet on the appearance of Ia and Ii mRNA. METHODS: Four litters were split at day 17; one half was weaned and the other remained with the mother until day 24. On day 23, 25, 27, and 29, enterocytes were isolated from full-length small intestine by vascular perfusion with 30 mmol/L ethylenediaminetetraacetic acid, and the RNA was extracted. RESULTS: Appearance of Ii and I-A beta was significantly delayed by late weaning, as judged by RNA hybridization blots (Ii chain) and complementary DNA amplification (I-A beta chain). In mice on elemental diets, the appearance of Ii and I-A beta chain was delayed compared with littermates reared on standard chow. Ii mRNA failed to appear in mice maintained on the elemental diet by day 40, despite normal growth. CONCLUSIONS: Appearance of mRNA for both Ia and Ii depends on the introduction of a complex diet and not the "stress" of weaning or elimination of breast milk. Introduction of foreign dietary antigens or development of an altered intestinal flora may contribute to this process. 相似文献
125.
CS Walpole R Wrigglesworth S Bevan EA Campbell A Dray IF James KJ Masdin MN Perkins J Winter 《Canadian Metallurgical Quarterly》1993,36(16):2381-2389
Structural variants of the hydrophobic side chain ("C region") of the capsaicin molecule have been incorporated into a series of vanillylamides and vanillylthioureas. These compounds have been tested in an in vitro assay for agonism (45Ca2+ influx into dorsal root ganglia neurones), previously shown to be predictive of analgesic activity. The results of this study have established the requirement for a hydrophobic substituent of limited size (molar refractivity, MR, < 55) in order to obtain high potency. Combination of the information gained here about the "C-region" of the capsaicin molecule with the studies described in the preceding two papers provides a rational basis for the design of compounds of increased potency. 相似文献
126.
Electron microscopic study was performed in the experiments on the rat liver while intravenously administering E. coli endotoxin. The dynamics of ultrastructural disorders during endotoxemia has been established and the role of "Kupffer cell-hepatocyte" microsystem in the liver detoxification function is shown. 相似文献
127.
EA Liberman AM Arzumanian MA Vladimirova LM Tsofina 《Canadian Metallurgical Quarterly》1976,21(3):476-481
"Zero-loop" of the molecular potential transformer of submitochondrial particles (SMP) is separated from the remaining electron transfer chain by rotenone, and its e.m.f. ET=0,003+RT/2F in [NADP X H] [NAD+]/[NADP+] [NAD X H] volts is used in the compensative method of measurement of the potential difference across the SMP membrane (delta USMP). The phospholipid membrane, measuring the concentration of the penetrating anions in the solution contained SMP, is used as "zero-indicators". This concentration drops monotonically with increase in delta USMP. Delta USMP is equal to ET when the addition of substrates of transhydrogenase reaction with definite ET does not change the potential across phospholipid membrane. 相似文献
128.
A novel method has been developed for the study of phospholipid exchange and fusion of phospholipid vesicles. Two homogeneous populations of single bilayer phosphatidylcholine vesicles of similar size but markedly different density have been prepared. "Dense" vesicles were made from brominated dioleoyl phosphatidylcholine. "Light" vesicles were prepared from dioleoyl phosphatidylcholine. The two populations were easily separated by density gradient centrifugation. Phosphatidylcholine exchange protein from beef liver was used to promote lecithin exchange between the vesicle populations. Only the lecithin of the external monolayers of the vesicles was available for exchange by exchange protein, implying that flip-flop of vesicle phosphatidylcholine did not take place at a detectable frequency. No spontaneous intervesicle phosphatidylcholine exchange was observed. However, the dense and light vesicles did spontaneously fuse, over several hours, to produce particles of hybrid density. 相似文献
129.
The culture system for in vitro evaluation of "colony forming units - culture (CFU-c)" is briefly outlined. This method offers a new approach to studies of proliferation and differentiation of hemopoietic progenitor cells, especially in disorders of granulopoiesis. From available published data it is evident that quantitation of CFU-c is also an indicator of diagnostic and prognostic value for assessment of various types of leukemia. The CFU-c assay has furthermore been introduced to test the viability and proliferating capacity of cryopreserved bone marrow, especially with a view to possible transfusion of stored autologous bone marrow as an adjuvant to cytostatic therapy. 相似文献
130.
This paper presents a formal framework, which is based on the notion of a serialization set, that enables to compose a set of consistency conditions into a more restrictive one. To exemplify the utility of this framework, a list of very basic consistency conditions is identified, and it is shown that various compositions of the basic conditions yield some of the most commonly used consistency conditions, such as sequential consistency, causal memory, and Pipelined RAM. The paper also lists several applications that can benefit from even weaker semantics than Pipelined RAM that can be expressed as a composition of a small subset of the basic conditions. 相似文献