全文获取类型
收费全文 | 2759篇 |
免费 | 40篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 14篇 |
综合类 | 4篇 |
化学工业 | 149篇 |
金属工艺 | 11篇 |
机械仪表 | 29篇 |
建筑科学 | 26篇 |
矿业工程 | 1篇 |
能源动力 | 29篇 |
轻工业 | 59篇 |
水利工程 | 6篇 |
石油天然气 | 1篇 |
无线电 | 131篇 |
一般工业技术 | 137篇 |
冶金工业 | 2002篇 |
原子能技术 | 10篇 |
自动化技术 | 195篇 |
出版年
2023年 | 17篇 |
2022年 | 41篇 |
2021年 | 65篇 |
2020年 | 40篇 |
2019年 | 52篇 |
2018年 | 42篇 |
2017年 | 33篇 |
2016年 | 43篇 |
2015年 | 26篇 |
2014年 | 37篇 |
2013年 | 47篇 |
2012年 | 47篇 |
2011年 | 54篇 |
2010年 | 32篇 |
2009年 | 33篇 |
2008年 | 26篇 |
2007年 | 19篇 |
2006年 | 15篇 |
2005年 | 12篇 |
2004年 | 13篇 |
2003年 | 11篇 |
2002年 | 8篇 |
2001年 | 9篇 |
2000年 | 8篇 |
1999年 | 81篇 |
1998年 | 720篇 |
1997年 | 392篇 |
1996年 | 242篇 |
1995年 | 121篇 |
1994年 | 119篇 |
1993年 | 119篇 |
1992年 | 25篇 |
1991年 | 24篇 |
1990年 | 12篇 |
1989年 | 18篇 |
1988年 | 11篇 |
1987年 | 15篇 |
1986年 | 10篇 |
1985年 | 18篇 |
1984年 | 2篇 |
1983年 | 5篇 |
1982年 | 3篇 |
1981年 | 9篇 |
1980年 | 13篇 |
1979年 | 2篇 |
1977年 | 32篇 |
1976年 | 67篇 |
1975年 | 5篇 |
1973年 | 3篇 |
1954年 | 1篇 |
排序方式: 共有2804条查询结果,搜索用时 0 毫秒
961.
962.
Wound repair is characterized by the presence of a fibrin-rich matrix, but the effect of fibrin on re-epithelialization remains unclear. In this study, we determined the effects of different fibrin matrices on cultured human neonatal keratinocytes. Using purified fibrinogen and fibrin gels generated by the enzymatic action of thrombin, batroxobin (it leads to retention of fibrinopeptide B), or Agkistrodon contortrix thrombin-like enzyme (ACTE; it leads to retention of fibrinopeptide A), we determined the effect of each of these matrices on keratinocyte morphology, attachment, spreading, and replication as compared to tissue culture plastic. Morphologically, keratinocytes seeded on fibrin surfaces were more rounded and formed three-dimensional structures. Specific cell attachment, as measured at either 37 degrees C or 4 degrees C, was not altered on the different fibrin substrates (P > .05) but was increased on fibrinogen and factor XIII cross-linked fibrin (P < .01). However, keratinocytes seeded on fibrin, regardless of the presence or absence of fibrinopeptides A or B, showed a marked decrease (up to 71%) in cell numbers by days 5 (P = .0357) and 10 (P = .0114). Keratinocyte spreading was decreased by 78.8% (P = .0006), 80.3% (P = .0001), and 89.2% (P = .0001) on thrombin-, batroxobin-, and ACTE-generated fibrin, respectively, but not on fibrinogen-coated dishes. However, either the addition of fibronectin or cross-linking of fibrin with factor XIII allowed full keratinocyte spreading to occur (P = .0002 and P = .0013, respectively). We conclude that fibrin inhibits keratinocyte spreading in the absence of other matrix or plasma proteins or cross-linking by factor XIII. 相似文献
963.
The present study was designed to reveal whether astrocytic activation following axotomy causes a numerical increase of nuclear bodies (NBs) in chicken astrocytes. Astrocytes in the spinal cord were activated by a unilateral spinal nerve transection. The frequency of NBs was calculated at the lateral motor columns of the normal group and at the ipsi- and contralateral sides of operated group. In the growing chickens, NBs of each astrocyte were a few and decreased steadily in number with age. In the operated chickens, the frequency of NBs elevated temporarily both in the ipsi- and contralateral sides, and reached its maximum value by 30 post-operative days. The frequency of NBs increased more prominently in the operated side than in the unoperated side. Thus, the present study provides the first evidence for a significant increase in the number of NBs in the hyperactive astrocytes caused by axotomy. 相似文献
964.
M Nomizu Y Kuratomi KM Malinda SY Song K Miyoshi A Otaka SK Powell MP Hoffman HK Kleinman Y Yamada 《Canadian Metallurgical Quarterly》1998,273(49):32491-32499
Laminin-1, a multifunctional glycoprotein of the basement membrane, consists of three different subunits, alpha1, beta1, and gamma1 chains. Previously, we used synthetic peptides to screen for biologically active sequences in the laminin alpha1 chain C-terminal globular domain (G domain) and identified several cell binding sequences (Nomizu, M., Kim, W. H., Yamamura, K., Utani, A., Song, S. Y., Otaka, A., Roller, P. P., Kleinman, H. K., and Yamada, Y. (1995) J. Biol. Chem. 270, 20583-20590). Here, we identify new cell binding sequences on the remainder of the laminin alpha1 chain by systematic peptide screening, using 208 overlapping synthetic peptides encompassing the central and N-terminal portions of the alpha1 chain. HT-1080 cell attachment activity to the peptides was evaluated using peptide-coated plastic substrates and peptide-conjugated Sepharose beads. Twenty five peptides showed cell attachment activities on either the peptide-coated plastic substrates and/or the peptide-conjugated Sepharose beads. A-13 (RQVFQVAYIIIKA) showed strongest cell attachment activity in both the assays. Cell attachment to 14 of the peptides was inhibited by heparin. EDTA and integrin antibodies inhibited cell adhesion to two of the peptides, A-13 and A-25, suggesting that these sites likely bind to integrins. These peptides inhibited cell attachment to laminin-1 but not to collagen I, suggesting these active sites are available on the intact molecule. Most of active sequences were localized on globular domains suggesting that these structures play a critical role in binding to cell-surface receptors. 相似文献
965.
An epoxide hydrolase from Rhodococcus erythropolis DCL14 catalyzes the hydrolysis of limonene-1,2-epoxide to limonene-1,2-diol. The enzyme is induced when R. erythropolis is grown on monoterpenes, reflecting its role in the limonene degradation pathway of this microorganism. Limonene-1,2-epoxide hydrolase was purified to homogeneity. It is a monomeric cytoplasmic enzyme of 17 kDa, and its N-terminal amino acid sequence was determined. No cofactor was required for activity of this colorless enzyme. Maximal enzyme activity was measured at pH 7 and 50 degrees C. None of the tested inhibitors or metal ions inhibited limonene-1,2-epoxide hydrolase activity. Limonene-1,2-epoxide hydrolase has a narrow substrate range. Of the compounds tested, only limonene-1,2-epoxide, 1-methylcyclohexene oxide, cyclohexene oxide, and indene oxide were substrates. This report shows that limonene-1,2-epoxide hydrolase belongs to a new class of epoxide hydrolases based on (i) its low molecular mass, (ii) the absence of any significant homology between the partial amino acid sequence of limonene-1,2-epoxide hydrolase and amino acid sequences of known epoxide hydrolases, (iii) its pH profile, and (iv) the inability of 2-bromo-4'-nitroacetophenone, diethylpyrocarbonate, 4-fluorochalcone oxide, and 1, 10-phenanthroline to inhibit limonene-1,2-epoxide hydrolase activity. 相似文献
966.
YW Song HA Kim HJ Baek EB Lee ES Chung KM Hong 《Canadian Metallurgical Quarterly》1998,20(11):669-677
We evaluated the effect of paclitaxel on the severity of autoimmunity in the murine model of systemic lupus erythematosus (SLE), NZB x NZW F1 mice. Fifteen 20 week old (NZB x NZW) F1 female mice were given a dose of 10 mg/kg paclitaxel by the intraperitoneal route on three alternate days followed by 7.5 mg/kg on three additional alternate days. This pattern of treatment was repeated every 4 weeks for a period of 28 weeks. 20 control mice were injected intraperitoneally with an equal volume of the vehicle used. Serum anti-double stranded DNA (dsDNA) antibody titers and the blood urea nitrogen (BUN) were significantly diminished in the paclitaxel treated group compared to the vehicle treated group. While the onset of proteinuria appeared to be delayed in the experimental group, the difference was not significant. Survival rate improved significantly in paclitaxel treated group (p = 0.04 by log-rank test). These results suggest that paclitaxel is beneficial in the suppression of autoimmunity in this strain of mice by reducing the anti-dsDNA antibody titer and the BUN, prolonging survival. 相似文献
967.
968.
969.
BG Bentz GK Haines AS vonSchlegell KM Elseth DG Hanson JA Radosevich 《Canadian Metallurgical Quarterly》1998,118(5):603-609
1. Renal specific targeting of the non-steroidal anti-inflammatory drug naproxen was obtained by coupling to the low-molecular-mass protein lysozyme. A previous study showed that conjugation to lysozyme resulted in a 70-fold increase of naproxen accumulation in the kidney with a subsequent renal release of the active metabolite naproxen-lysine.2. In the present study we questioned whether naproxen-lysozyme is active in the rat kidney, inhibiting the urinary excretion of prostaglandin E2 and renal sodium and water excretion in salt-restricted baseline conditions as well as during frusemide treatment.3.A high dose of free naproxen (10 mg.day-1. kg-1) did not affect prostaglandin E2 excretion in baseline conditions (naproxen, 11+/-1 ng/8 h; vehicle, 13+/-4 ng/8 h), whereas sodium and water excretion were, respectively, 3.0 and 1.6 times lower in the naproxen group (P<0.05). Naproxen completely prevented the frusemide-induced increase (3-fold) in prostaglandin E2 excretion (naproxen 6.6+/-1.1 ng/8 h, vehicle 40+/-12 ng/8 h, P<0. 005). Frusemide-stimulated natriuresis and diuresis were, respectively, 1.6 (P<0.05) and 1.8 times (P<0.005) lower in the naproxen group.4.A dose of 2 mg.day-1.kg-1 lysozyme-conjugated naproxen did not affect prostaglandin E2 excretion in baseline conditions (conjugate, 18+/-2 ng/8 h; vehicle, 24+/-5 ng/8 h). The conjugate also had no effect on sodium and water excretion. However, the naproxen conjugate completely prevented the frusemide-induced increase (2-fold) in prostaglandin E2 excretion (conjugate, 16+/-3 ng/8 h; vehicle, 48+/-13 ng/8 h, P<0.05). Surprisingly, frusemide-induced natriuresis and diuresis were not affected by the conjugate.5. In conclusion, a renal specific delivery of the non-steroidal anti-inflammatory drug naproxen using lysozyme results in an inhibitory effect on renal prostaglandin E2 synthesis but does not affect the excretion of sodium and water, in contrast to free naproxen. 相似文献
970.
The survival of dorsal root ganglion (DRG) neurons, both in vivo and in vitro, is dependent on the availability of nerve growth factor (NGF) for a transient period early in development after which these neurons become independent of NGF for survival. The precise molecular mechanism by which developing DRG neurons gain independence from NGF has not been determined. We used an in vitro model of DRG neuronal development to test hypotheses that independence from NGF in mature DRG neurons could be caused by developmental regulation of either elements of the NGF withdrawal signal transduction pathway or of proteins important for activation of the apoptosis output pathway. Interruption of phosphotidylinositol-3 kinase activation, by treatment with the specific inhibitor LY294002, resulted in apoptosis in immature but not mature DRG neurons in a manner similar to that observed with NGF withdrawal. Further downstream along the signal transduction pathway, c-JUN phosphorylation occurred in both immature and mature DRG neurons after NGF withdrawal or treatment with LY294002, despite the fact that the older neurons did not undergo apoptosis. In contrast, the ratio of expression of the proapoptotic gene bax to antiapoptotic gene bcl-xL was many times higher in immature than mature neurons, both in vivo and in vitro. Taken together, these results strongly suggest that developmental regulation of NGF withdrawal-induced apoptosis in DRG occurs via control of the relative level of expression of members of the bcl-2 gene family. 相似文献