全文获取类型
收费全文 | 1480篇 |
免费 | 22篇 |
专业分类
电工技术 | 2篇 |
综合类 | 1篇 |
化学工业 | 139篇 |
金属工艺 | 44篇 |
机械仪表 | 42篇 |
建筑科学 | 5篇 |
能源动力 | 20篇 |
轻工业 | 26篇 |
石油天然气 | 2篇 |
无线电 | 79篇 |
一般工业技术 | 126篇 |
冶金工业 | 951篇 |
原子能技术 | 7篇 |
自动化技术 | 58篇 |
出版年
2023年 | 1篇 |
2022年 | 9篇 |
2021年 | 16篇 |
2020年 | 9篇 |
2019年 | 15篇 |
2018年 | 17篇 |
2017年 | 17篇 |
2016年 | 12篇 |
2015年 | 17篇 |
2014年 | 24篇 |
2013年 | 50篇 |
2012年 | 54篇 |
2011年 | 47篇 |
2010年 | 31篇 |
2009年 | 25篇 |
2008年 | 31篇 |
2007年 | 24篇 |
2006年 | 15篇 |
2005年 | 23篇 |
2004年 | 17篇 |
2003年 | 22篇 |
2002年 | 13篇 |
2001年 | 15篇 |
2000年 | 9篇 |
1999年 | 46篇 |
1998年 | 323篇 |
1997年 | 188篇 |
1996年 | 125篇 |
1995年 | 70篇 |
1994年 | 62篇 |
1993年 | 44篇 |
1992年 | 13篇 |
1991年 | 12篇 |
1990年 | 9篇 |
1989年 | 19篇 |
1988年 | 13篇 |
1987年 | 10篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1978年 | 1篇 |
1977年 | 8篇 |
1976年 | 16篇 |
1975年 | 2篇 |
1971年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有1502条查询结果,搜索用时 15 毫秒
11.
12.
13.
14.
Rolipram inhibited U937 cell phosphodiesterase-4 in either the presence or absence of saturating (100 micrograms/ml) phosphatidic acid in an apparently phospholipid-independent manner, exhibiting similar kinetics (Ki values = 0.41 and 0.59 microM, respectively). At low concentrations (10 and 100 nM), however, rolipram caused a rightward shift of the phosphatidic acid concentration-response curve for phosphodiesterase-4 activation, suppressing activation by up to 70%. Maximum inhibition of phosphodiesterase-4 activation occurred at phosphatidic acid concentrations of 5-40 micrograms/ml. The results suggest that rolipram is capable of inhibiting phosphodiesterase-4 by both phospholipid-dependent and phospholipid-independent mechanisms. 相似文献
15.
16.
MR Farnoud M Kujas P Derome J Racadot F Peillon JY Li 《Canadian Metallurgical Quarterly》1994,424(1):75-82
Previously, the species complex Oncomelania hupensis, individuals of which act as intermediate hosts for the human bloodfluke Schistosoma japonicum, has been characterised by morphological and isoenzyme criteria. We have examined genetic variation between and within three subspecies of Oncomelania hupensis, i.e. O. h. hupensis (China), O. h. quadrasi (Philippines) and O. h. nosophora (Japan), by direct means using a PCR-based RFLP method. The subspecies of O. hupensis were readily distinguished by their characteristic restriction patterns, supporting isoenzyme data which suggests these may warrant species-specific status. No genetic variation was observed between O. h. quadrasi from different islands within the Philippines. In contrast, geographical isolates of O. h. hupensis differed markedly by this method indicating several genetically distinct populations of O. h. hupensis occur in China. 相似文献
17.
We have made reasonably comprehensive measurements of action potential activity in the Aplysia californica abdominal ganglion to determine the amount of feedback the central nervous system (CNS) receives from a movement which it initiates. Voltage-sensitive dye measurements of action potential activity of cells in the ganglion were made during the gill-withdrawal reflex elicited by siphon stimulation. We compared recordings in two situations which differed dramatically in the amount the gill moved. In the control sea water, the gill withdrawal was normal; in low-Ca2+, high-Mg2+ sea water, the gill movement was blocked. Both the timing and the number of spikes of the individual neurons were similar in the two situations. Histograms of the summed spike activity versus time and histograms of the number of active neurons versus time in the two conditions were also similar. Finally, two numerical measures of trial-to-trial differences, a paired t-test and a measure we named fractional similarity, did not indicate larger differences between two trials in the different sea waters than two trials in the same sea water. Feedback from sensory neurons activated by the gill movement itself does not make a large contribution to the spike activity in the abdominal ganglion. Apparently the Aplysia CNS issues the command for the withdrawal and does not make adjustments for the magnitude of the actual withdrawal. It may not even receive the information necessary for such adjustments to be made. A second motivation for these experiments was to test whether removing the feedback might simplify the neuronal activity that occurs during the gill-withdrawal reflex. This did not occur. 相似文献
18.
Spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats that had been on a low sodium diet for 3 days were given 1.5 mmol sodium chloride kg-1 body weight either orally or intravenously. The rats receiving an oral sodium load showed a greater natriuresis than those receiving the same saline load intravenously. No increase of renal sodium excretion was observed when the rats received a hypertonic mannitol solution orally. The cumulative sodium excretion during the 8 h following oral loading was two to three times larger in SHR than in WKY, whereas no difference between strains could be demonstrated after giving saline intravenously. Furthermore, after switching from normal to low sodium diet the rate of decrease of renal sodium excretion was greater in SHR than in WKY rats. It is proposed that there exists a gastrointestinal sensory mechanism for sodium controlling the renal sodium excretion. Furthermore, it is suggested that the function of this mechanism differs between SHR and WKY. 相似文献
19.
JY Scoazec JF Flejou A D'Errico M Fiorentino A Zamparelli AF Bringuier G Feldmann WF Grigioni 《Canadian Metallurgical Quarterly》1996,24(5):1128-1136
We have analyzed the composition of the tumor stroma and the expression of cell-matrix and cell-cell adhesion molecules in 11 cases of fibrolamellar carcinoma of the liver (FLC), in comparison with 34 cases of hepatocellular carcinoma and 8 cases of focal nodular hyperplasia. Fibrolamellar carcinoma was characterized by the presence of large amounts of tenascin in tumor stroma and by the scarce expression of basement membrane components at the contact of neoplastic clusters. Like normal hepatocytes, neoplastic cells constantly expressed the alpha1 integrin chain, lacked the beta4 integrin chain, and coexpressed E-cadherin and the hepatocyte N-related cadherin. Abnormalities in the expression of cell adhesion molecules, including altered cadherin expression, alphaV integrin chain induction, and CD44 expression, were detected in the majority of cases. The composition of the tumor stroma and the pattern of expression of cell adhesion molecules in fibrolamellar carcinoma were reminiscent of those observed in grade III and grade IV hepatocellular carcinomas. Our results therefore show that, despite its slow local growth and good prognosis, fibrolamellar carcinoma expresses many characteristics usually associated with clinically aggressive malignancies. Further studies are needed to identify the factors responsible for the apparent dissociation between clinical behavior and biological characteristics in this tumor. 相似文献
20.
Beliefs about human nature, adult education, adult learners, and moral commitment are at the heart of the educator-learner agreement. In continuing nursing education, it is the point where professional values, morals, and ethical principles meet. Using Husteds' bioethical decision-making model, the values, beliefs, and actions within the educator-learning agreement are identified and organized by the bioethical standards. By relating the bioethical standards to practice, continuing nurse educators can find their own basis for practice and work toward attaining a consistent professional ethical orientation. 相似文献