全文获取类型
收费全文 | 10253篇 |
免费 | 102篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 139篇 |
综合类 | 4篇 |
化学工业 | 861篇 |
金属工艺 | 110篇 |
机械仪表 | 141篇 |
建筑科学 | 164篇 |
矿业工程 | 33篇 |
能源动力 | 104篇 |
轻工业 | 691篇 |
水利工程 | 42篇 |
石油天然气 | 23篇 |
无线电 | 793篇 |
一般工业技术 | 983篇 |
冶金工业 | 5444篇 |
原子能技术 | 109篇 |
自动化技术 | 716篇 |
出版年
2021年 | 47篇 |
2019年 | 45篇 |
2018年 | 50篇 |
2017年 | 57篇 |
2016年 | 73篇 |
2015年 | 51篇 |
2014年 | 82篇 |
2013年 | 184篇 |
2012年 | 164篇 |
2011年 | 226篇 |
2010年 | 195篇 |
2009年 | 206篇 |
2008年 | 227篇 |
2007年 | 232篇 |
2006年 | 199篇 |
2005年 | 202篇 |
2004年 | 185篇 |
2003年 | 165篇 |
2002年 | 142篇 |
2001年 | 148篇 |
2000年 | 163篇 |
1999年 | 276篇 |
1998年 | 1390篇 |
1997年 | 839篇 |
1996年 | 664篇 |
1995年 | 359篇 |
1994年 | 328篇 |
1993年 | 427篇 |
1992年 | 166篇 |
1991年 | 177篇 |
1990年 | 171篇 |
1989年 | 193篇 |
1988年 | 167篇 |
1987年 | 146篇 |
1986年 | 169篇 |
1985年 | 152篇 |
1984年 | 87篇 |
1983年 | 93篇 |
1982年 | 92篇 |
1981年 | 89篇 |
1980年 | 89篇 |
1979年 | 78篇 |
1978年 | 86篇 |
1977年 | 177篇 |
1976年 | 330篇 |
1975年 | 61篇 |
1974年 | 57篇 |
1973年 | 53篇 |
1972年 | 37篇 |
1971年 | 36篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Ionel D.M. Popescu M. Dellinger S.J. Miller T.J.E. Heideman R.J. McGilp M.I. 《Industry Applications, IEEE Transactions on》2006,42(3):658-667
A model of core losses, in which the hysteresis coefficients are variable with the frequency and induction (flux density) and the eddy-current and excess loss coefficients are variable only with the induction, is proposed. A procedure for identifying the model coefficients from multifrequency Epstein tests is described, and examples are provided for three typical grades of non-grain-oriented laminated steel suitable for electric motor manufacturing. Over a wide range of frequencies between 20-400 Hz and inductions from 0.05 to 2 T, the new model yielded much lower errors for the specific core losses than conventional models. The applicability of the model for electric machine analysis is also discussed, and examples from an interior permanent-magnet and an induction motor are included. 相似文献
62.
In a series of experiments over 3 yr, relatively low doses of selenium and vitamin E were injected intramuscularly 3 wk prepartum to pregnant Israeli-Holstein dairy cows in a high-producing herd (9000 kg milk/yr) with a history of retained placenta in 17% of the primiparous and 28% of the multiparous animals, as recorded for the 12 mo preceding the study. Selenium ranged from .035 to .109 ppm in the prepartum diet and from .160 to .200 ppm in the postpartum diet. Doses of selenium ranging from 2.3 to 23.0 mg reduced the incidence of retained placenta in 186 primiparous and in 428 multiparous to 7 and 15%, which was half of that of controls. Low doses of selenium (2.3 to 4.6 mg) tended to be more effective than higher ones. Selenium alone was at least as effective as a combination of selenium and vitamin E. Dosage, timing, mechanism, and interactions of selenium with other factors in reducing the incidence of retained placenta need clarification. 相似文献
63.
64.
Self-disclosure plays a central role in the development and maintenance of relationships. One way that researchers have explored these processes is by studying the links between self-disclosure and liking. Using meta-analytic procedures, the present work sought to clarify and review this literature by evaluating the evidence for 3 distinct disclosure-liking effects. Significant disclosure-liking relations were found for each effect: (1) People who engage in intimate disclosures tend to be liked more than people who disclose at lower levels, (2) people disclose more to those whom they initially like, and (3) people like others as a result of having disclosed to them. In addition, the relation between disclosure and liking was moderated by a number of variables, including study paradigm, type of disclosure, and gender of the discloser. Taken together, these results suggest that various disclosure-liking effects can be integrated and viewed as operating together within a dynamic interpersonal system. Implications for theory development are discussed, and avenues for future research are suggested. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
65.
Nucleation-limited aggregation in fractal growth 总被引:1,自引:0,他引:1
66.
OBJECTIVE: The authors report the use of multiple implanted intraspinal port and catheter systems per test animal to study the in vivo functional characteristics and reliability of a new implantable spinal drug delivery port system. METHODS: Four ewes were each implanted with two epidural and one subarachnoid silicone elastomer catheters at the lumbar level. Each catheter was connected in series to one of three Therex filtered spinal delivery ports implanted subcutaneously in a similar grid pattern in each ewe to facilitate percutaneous identification. Saline (2 ml) was injected 3 times weekly in each port. The ease of injection and behavioral responses were recorded for 207-213 days of implantation until sacrifice/necropsy. RESULTS: All ports functioned reliably during the study. However, injection through two of the four subarachnoid catheters resulted in behavioral withdrawal responses intermittently. This behavioral pattern was much less common after epidural port injections. All four subarachnoid and four of eight epidural port and catheter systems were tested with local anesthetic just before sacrifice. Motor block was observed in three of four subarachnoid and three of four epidural port and catheter systems tested. Integrity of the other four epidural ports was tested by injection of methylene blue at sacrifice. This dye did not distribute in the epidural space in one of the latter four epidural ports (not local anesthetic tested) because of a concentric fibrotic reaction about the catheter. Similar fibrotic reactions surrounded the catheters that failed a functional test with local anesthetic. CONCLUSIONS: The implantable intraspinal port system tested functions reliably under repetitive percutaneous access. However, filtering such ports, though desirable to prevent entry of debris into the spinal canal, did not eliminate pericatheter chronic subarachnoid and epidural reaction. The number of test animals required to test 12 ports chronically was reduced by two-thirds without undue trauma to the individual test subject. Chronic percutaneous injection of an implanted subarachnoid system is feasible but may be associated with behavioral effects similar to that seen with chronic epidural systems. Fibrosis around chronic silicone catheters limited functional utility in one-fourth of the implanted test systems. Further study of the potential reactivity of chronic epidural and subarachnoid catheters is indicated. 相似文献
67.
RW Sidwell DF Smee RP Warren JH Huffman BJ Gilbert RA Burger FC Pearson 《Canadian Metallurgical Quarterly》1993,20(4):279-292
ImuVert, a sterile preparation composed primarily of Serratia marcescens membrane vesicles and ribosomes, was significantly inhibitory to murine cytomegalovirus (MCMV) infections in BALB/c mice. Antiviral activity was manifested as increased survivor number and decreased recoverable virus titers in spleens, lungs and salivary glands. Treatments were intraperitoneal (i.p.) beginning 24 h pre, 4 h post- or 24 h post-virus inoculation and then repeated 4 days later. Doses of 5, 16 or 50 micrograms/mouse were effective; 160 micrograms/mouse, which caused host weight loss in toxicity controls, was not inhibitory to the infection. A single i.p. treatment of mice substantially augmented natural killer (NK) cell activity and increased total B-cells, while reducing total T- and T-helper cells. A late (48 h) decline in T-cell function and transient increases in B-cell function were observed in the treated animals. Serum interferon was not induced. Mice pretreated with anti-asialo GM1 antibody to reduce their NK cell populations, then infected with MCMV and treated with ImuVert were protected to the same degree as normal animals. Severe combined immunodeficient mice infected with MCMV and treated with ImuVert were not protected from the infection. These data suggest ImuVert to act by a mechanism other than NK cell activation in preventing MCMV infections. 相似文献
68.
LA Miller 《Canadian Metallurgical Quarterly》1998,13(4):717-25, iv
Medical networks offer discounted fees, control of the workers' compensation case, quality monitoring, and managed care services. As channeling of workers' compensation cases to networks increases, credentialed physicians will benefit. 相似文献
69.
It was proposed that individuals' responses to information regarding their relative position in a performance distribution would depend on how they frame the information. To the degree that they focus selectively on the positive features of the feedback (i.e., the number of others who performed worse than them) rather than the negative features (i.e., the number of others who performed better than them) they should report higher ability levels and more positive affective reactions. In Study I, Ss received feedback indicating that they occupied a particular percentile standing in either a large or small distribution. Individuals with negative orientations (depressives and pessimists) reported lower ability levels as a function of increases in comparison group size, whereas individuals with positive orientations (nondepressives and optimists) reported higher ability levels. Presumably, these effects occurred because negatively oriented persons focused on the negative features of the feedback and positively oriented persons focused on the positive features of the feedback. The results of Study 2 support this explanation. Implications for the social comparison literature are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
70.