全文获取类型
收费全文 | 11120篇 |
免费 | 359篇 |
国内免费 | 41篇 |
学科分类
工业技术 | 11520篇 |
出版年
2023年 | 66篇 |
2022年 | 144篇 |
2021年 | 174篇 |
2020年 | 120篇 |
2019年 | 136篇 |
2018年 | 187篇 |
2017年 | 128篇 |
2016年 | 232篇 |
2015年 | 216篇 |
2014年 | 287篇 |
2013年 | 659篇 |
2012年 | 469篇 |
2011年 | 640篇 |
2010年 | 493篇 |
2009年 | 460篇 |
2008年 | 501篇 |
2007年 | 490篇 |
2006年 | 411篇 |
2005年 | 374篇 |
2004年 | 347篇 |
2003年 | 263篇 |
2002年 | 273篇 |
2001年 | 213篇 |
2000年 | 193篇 |
1999年 | 201篇 |
1998年 | 436篇 |
1997年 | 271篇 |
1996年 | 245篇 |
1995年 | 207篇 |
1994年 | 168篇 |
1993年 | 181篇 |
1992年 | 158篇 |
1991年 | 109篇 |
1990年 | 134篇 |
1989年 | 120篇 |
1988年 | 125篇 |
1987年 | 80篇 |
1986年 | 74篇 |
1985年 | 107篇 |
1984年 | 114篇 |
1983年 | 73篇 |
1982年 | 83篇 |
1981年 | 99篇 |
1980年 | 81篇 |
1979年 | 96篇 |
1978年 | 82篇 |
1977年 | 84篇 |
1976年 | 92篇 |
1975年 | 70篇 |
1973年 | 65篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
22.
Visual and auditory stimulus discrimination tasks, analogous to those used in the Reitan-Klove Sensory Perceptual Examination, were performed by 12 cocaine-dependent and 5 alcohol-dependent patients after 1 week, 3 weeks, and 3 months of verified abstinence. Sixteen control subjects, who were not substance-dependent, performed the same tasks after comparable intervals. During each task, either visual or auditory stimuli were presented in the left, in the right, or in both sensory fields. A simple key press was made to discriminate these conditions. Cocaine-dependent patients responded more slowly than control subjects during both tasks. The reaction-time slowing persisted across all three sessions, spanning a 3-month period of abstinence. There were no significant differences between the cocaine-dependent and control groups in response accuracy. In the context of other findings, these findings are interpreted as reflecting an enduring effect of prior cocaine dependence on motor as opposed to sensory functioning. 相似文献
23.
Accumulation of ochratoxin A in rat kidney in vivo and in cultivated renal epithelial cells in vitro
Biological applications of triplex forming oligonucleotides will require the development of oligomers with high avidity and specificity. We examined the binding enhancement resulting from intercalator conjugation to both parallel design (polythymidine T15) and antiparallel design (polypurine AG15, for binding a 15 base pair polypurine-polypyrimidine sequence in the IL-2R alpha gene enhancer) oligomers under various ionic strength and temperature conditions. Oligonucleotides were conjugated through a urea link to 6,9 diamino-3-methoxy acridine (to give T15C and AG15C). Intercalator conjugation dramatically enhanced the specific triplex binding avidity (Kd = 5 nM for AG15C and 275 nM for T15C at 25 degrees C, compared to 2 microM for AG15 and > 50 microM for T15 at 25 degrees C), without detectable binding to an inappropriate target sequence. Surprisingly, triplex formation with AG15C occurred at lower Mg2+ concentrations than with T15C. AG15 and AG15C showed rapid Mg2+ dependent self association, but not T15C or T15. T15C triplex formation occurred rapidly (completion in less than 4 min), while AG15C bound to its target sequence more slowly over 20-24 h. Thus, binding constants in the low nanomolar range are now achievable with intercalator conjugated polypurine antiparallel binding oligonucleotides, a prerequisite for biological applications of such agents. 相似文献
24.
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
25.
JF Delaloye S Leyvraz E Outcha Adjahoto J Bauer P De Grandi 《Canadian Metallurgical Quarterly》1996,19(2):204-206
We report two cases of metastatic non-functioning pancreatic endocrine tumour with very elevated plasma levels of alpha-fetoprotein. In these two cases, serial plasma levels of alpha-fetoprotein, initially normal, correlated well with hepatic tumour progression and were associated with fatal outcome. These results suggest that elevated plasma concentration of alpha-fetoprotein may be caused by metastatic pancreatic endocrine tumour and than alpha-fetoprotein serial measurement may be useful in prognostic evaluation. 相似文献
26.
27.
Many real-world problems are multi-objective optimization problems and evolutionary algorithms are quite successful on such problems. Since the task is to compute or approximate the Pareto front, multi-objective optimization problems are considered as more difficult than single-objective problems. One should not forget that the fitness vector with respect to more than one objective contains more information that in principle can direct the search of evolutionary algorithms. Therefore, it is possible that a single-objective problem can be solved more efficiently via a generalized multi-objective model of the problem. That this is indeed the case is proved by investigating the computation of minimum spanning trees.This work was supported by the Deutsche Forschungsgemeinschaft (DFG) as part of the Collaborative Research Center Computational Intelligence (SFB 531) and by the German-Israeli Foundation (GIF) in the project Robustness Aspects of Algorithms. 相似文献
28.
Acceptance, the willingness to experience thoughts, feelings, and physiological sensations without having to control them or let them determine one's actions, is a major individual determinant of mental health and behavioral effectiveness in a more recent theory of psychopathology. This 2-wave panel study examined the ability of acceptance also to explain mental health, job satisfaction, and performance in the work domain. The authors hypothesized that acceptance would predict these 3 outcomes 1 year later in a sample of customer service center workers in the United Kingdom (N = 412). Results indicated that acceptance predicted mental health and an objective measure of performance over and above job control, negative affectivity, and locus of control. These beneficial effects of having more job control were enhanced when people had higher levels of acceptance. The authors discuss the theoretical and practical relevance of this individual characteristic to occupational health and performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
29.
Collage grammars are context-free devices which generate picture languages consisting of collages—sets of parts, where a part is a set of points in a given space. In order to show that certain collage languages cannot be generated, the well-known pumping technique turns out to be rather useless. To circumvent this difficulty, other necessary criteria for context-freeness are established in this paper. Roughly speaking, these criteria reveal that (1) the collages in a context-free collage language can be deflated stepwise in such a manner that the difference between subsequent collages in the resulting chain is small and (2) the volume of parts can grow or shrink only exponentially. 相似文献
30.