全文获取类型
收费全文 | 2265篇 |
免费 | 26篇 |
专业分类
电工技术 | 22篇 |
化学工业 | 136篇 |
金属工艺 | 14篇 |
机械仪表 | 19篇 |
建筑科学 | 53篇 |
矿业工程 | 2篇 |
能源动力 | 15篇 |
轻工业 | 94篇 |
水利工程 | 4篇 |
无线电 | 198篇 |
一般工业技术 | 205篇 |
冶金工业 | 1385篇 |
原子能技术 | 14篇 |
自动化技术 | 130篇 |
出版年
2021年 | 12篇 |
2020年 | 12篇 |
2019年 | 8篇 |
2018年 | 14篇 |
2017年 | 9篇 |
2016年 | 11篇 |
2015年 | 8篇 |
2014年 | 23篇 |
2013年 | 36篇 |
2012年 | 27篇 |
2011年 | 38篇 |
2010年 | 36篇 |
2009年 | 47篇 |
2008年 | 38篇 |
2007年 | 39篇 |
2006年 | 40篇 |
2005年 | 25篇 |
2004年 | 28篇 |
2003年 | 36篇 |
2002年 | 27篇 |
2001年 | 28篇 |
2000年 | 22篇 |
1999年 | 71篇 |
1998年 | 408篇 |
1997年 | 210篇 |
1996年 | 130篇 |
1995年 | 99篇 |
1994年 | 89篇 |
1993年 | 89篇 |
1992年 | 27篇 |
1991年 | 23篇 |
1990年 | 27篇 |
1989年 | 39篇 |
1988年 | 25篇 |
1987年 | 40篇 |
1986年 | 35篇 |
1985年 | 38篇 |
1984年 | 22篇 |
1983年 | 19篇 |
1982年 | 19篇 |
1981年 | 25篇 |
1980年 | 18篇 |
1979年 | 23篇 |
1978年 | 9篇 |
1977年 | 39篇 |
1976年 | 95篇 |
1975年 | 17篇 |
1974年 | 12篇 |
1973年 | 10篇 |
1971年 | 11篇 |
排序方式: 共有2291条查询结果,搜索用时 15 毫秒
1.
Two Caribbean hair sheep breeds, the St. Croix (SC) and Barbados Blackbelly (BB), are found in the United States, and the SC has led to the development of the Katahdin (K), a synthetic breed of hair sheep. These breeds have mature ewe BW ranging from 32 to 54 kg (for BB and SC) and from 55 to 73 kg (K). Hair sheep and hair sheep crosses have lower rectal temperatures and respiration rates than wool breeds and a lower DMI and water intake. There are indications of increased resistance to internal parasites in hair sheep. Although hair sheep are seasonal breeders under U.S. photoperiodic conditions, they tend to perform better under accelerated lambing systems than traditional wool breeds. Fertility, prolificacy, and lamb survival is high in BB and SC, but hair x wool crossbred ewes tend to have a higher level of fertility than hair and wool parent breeds. Ewe productivity is also higher in hair x wool crosses than in wool crosses, particularly when adjusted for ewe BW or under accelerated lambing systems. Hair sheep have a lower ADG and intake of high-energy diets, as well as a lower gain/feed ratio, than wool breeds. Growth rates tend to be higher in SC than in BB. Differences in carcass characteristics are inconsistent between hair and wool breeds. Production characteristics of hair sheep, particularly hair x wool crosses, make them suitable for low-input, sustainable production systems that do not require high growth rates and large carcasses. There is a need to preserve the existing U.S. hair sheep germplasm base in support of such systems. 相似文献
2.
Transport properties of disordered continuum systems 总被引:1,自引:0,他引:1
3.
On the existence and synthesis of multifinger positive grips 总被引:5,自引:0,他引:5
We study the criteria under which an object can be gripped by a multifingered dexterous hand, assuming no static friction between the object and the fingers; such grips are calledpositive grips. We study three cases in detail: (i) the body is at equilibrium, (ii) the body is under some constant external force/torque, and (iii) the body is under a varying external force/torque. In each case we obtain tight bounds on the number of fingers needed to obtain grip.We also present efficient algorithms to synthesize such positive grips for bounded polyhedral/polygonal objects; the number of fingers employed in the grips synthesized by our algorithms match the above bounds. The algorithms run in time linear in the number of faces/sides.The paper may be of independent interest for its presentation of algorithms arising in the study of positive linear spaces.Work on this paper has been supported by Office of Naval Research Grant N00014-82-K.-0381, National Science Foundation Grant No. NSF-DCR-83-20085, and by grants from the Digital Equipment Corporation, and the IBM Corporation. 相似文献
4.
P Trifillis K Adachi T Yamaguchi E Schwartz S Surrey 《Canadian Metallurgical Quarterly》1996,271(43):26931-26938
We previously identified five delta-globin gene alleles associated with reduced hemoglobin (Hb) A2 (Trifillis, P., Ioannou, P., Schwartz, E., and Surrey, S. (1991) Blood 78, 3298-3305). We have now evaluated functional consequences of the changes after expression in COS-1 cells to monitor effects on RNA splicing. In addition, variant Hb A2 tetramers were expressed in yeast to assess effects of amino acid changes on oxygen binding and stability to heat and mechanical agitation. The G --> T change at codon 27 and the A --> G change in IVS-2 both affect RNA splicing, whereas the C --> T change at codon 97 and the AT deletion in IVS-2 have no effect. Oxygen equilibrium curves of the Hb A2 variants expressed in yeast were similar to that of wild type Hb A2. None of the three variant Hb A2 tetramers (Thr --> Ile at codon 4 (Hb deltaT4I), Ala --> Ser at codon 27 (Hb deltaA27S), and Arg --> Cys at codon 116 (Hb deltaR116C)) showed decreased heat stability compared with Hb A2, whereas the Hb deltaT4I variant showed highest instability to mechanical agitation. Co-expression in yeast of alpha-globin chain and the delta-chain variant containing a Leu --> Pro change at codon 141 yielded no identifiable tetramers, suggesting lack of assembly or severe tetramer instability. These studies show the probable cause for decreased Hb A2 for two alleles is due to defective splicing, whereas decreased protein stability, increased tetramer association with red cell membranes, increased interdisulfide bond formation of delta-chains, which inhibits assembly with alpha-chains, and/or reduced assembly is suggested for the other three alleles. 相似文献
5.
We report two patients with ileal carcinoid tumours which were associated with polyps due to mucosal granulation tissue proliferation. In both cases the tumours had extensively infiltrated the small bowel wall and mesentery, and one had hepatic metastases. The mucosal surface of each specimen showed numerous, pale brown, sessile polyps which were restricted to the intestinal segment involved by carcinoid tumour, although not always closely related to neoplastic cells. The polyps were formed by the proliferation of capillaries, smooth muscle cells and myofibroblasts as demonstrated by immunohistochemistry and electronmicroscopy. 相似文献
6.
TJ Meyer SE Eveloff MS Bauer WA Schwartz NS Hill RP Millman 《Canadian Metallurgical Quarterly》1994,105(4):1211-1216
Sleep deprivation and fragmentation occurring in the hospital setting may have a negative impact on the respiratory system by decreasing respiratory muscle function and ventilatory response to CO2. Sleep deprivation in a patient with respiratory failure may, therefore, impair recovery and weaning from mechanical ventilation. We postulate that light, sound, and interruption levels in a weaning unit are major factors resulting in sleep disorders and possibly circadian rhythm disruption. As an initial test of this hypothesis, we sampled interruption levels and continuously monitored light and sound levels for a minimum of seven consecutive days in a medical ICU, a multiple bed respiratory care unit (RCU) room, a single-bed RCU room, and a private room. Light levels in all areas maintained a day-night rhythm, with peak levels dependent on window orientation and shading. Peak sound levels were extremely high in all areas representing values significantly higher than those recommended by the Environmental Protection Agency as acceptable for a hospital environment. The number of sound peaks greater than 80 decibels, which may result in sleep arousals, was especially high in the intensive and respiratory care areas, but did show a day-night rhythm in all settings. Patient interruptions tended to be erratic, leaving little time for condensed sleep. We conclude that the potential for environmentally induced sleep disruption is high in all areas, but especially high in the intensive and respiratory care areas where the negative consequences may be the most severe. 相似文献
7.
Abe Schwartz Lili Wang Edward Early Adolfas Gaigalas Yu-zhong Zhang Gerald E. Marti Robert F. Vogt 《Journal of research of the National Institute of Standards and Technology》2002,107(1):83-91
The quantitation of fluorescence radiance may at first suggest the need to obtain the number of fluorophore that are responsible for the measured fluorescence radiance. This goal is beset by many difficulties since the fluorescence radiance depends on three parameters 1) the probability of absorbing a photon (molar extinction), 2) the number of fluorophores, and 3) the probability of radiative decay of the excited state (quantum yield). If we use the same fluorophore in the reference solution and the analyte then, to a good approximation, the molar extinction drops out from the comparison of fluorescence radiance and we are left with the comparison of fluorescence yield which is defined as the product of fluorophore concentration and the molecular quantum yield. The equality of fluorescence yields from two solutions leads to the notion of equivalent number of fluorophores in the two solutions that is the basis for assignment of MESF (Molecules of Equivalent Soluble Fluorophore) values. We discuss how MESF values are assigned to labeled microbeads and by extension to labeled antibodies, and how these assignments can lead to the estimate of the number of bound antibodies in flow cytometer measurements. 相似文献
8.
9.
10.
Introduces this special issue of Psychoanalytic Psychology. This special issue on Women, Psychoanalysis, and Gender is a commemoration of the capability, influence, acceptance, and authority of women in the community of psychoanalysis. In this issue, we turn to both new and more established voices in an expanded arena of gender, culture, and psychoanalysis. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献