全文获取类型
收费全文 | 645347篇 |
免费 | 69721篇 |
国内免费 | 940篇 |
出版年
2018年 | 6307篇 |
2017年 | 6069篇 |
2016年 | 8451篇 |
2015年 | 11289篇 |
2014年 | 13361篇 |
2013年 | 18454篇 |
2012年 | 21276篇 |
2011年 | 22180篇 |
2010年 | 14899篇 |
2009年 | 13509篇 |
2008年 | 19571篇 |
2007年 | 20089篇 |
2006年 | 18942篇 |
2005年 | 18029篇 |
2004年 | 17991篇 |
2003年 | 17091篇 |
2002年 | 16629篇 |
2001年 | 28360篇 |
2000年 | 28281篇 |
1999年 | 22168篇 |
1998年 | 7603篇 |
1997年 | 7670篇 |
1996年 | 7321篇 |
1995年 | 7157篇 |
1994年 | 6870篇 |
1993年 | 6808篇 |
1992年 | 18283篇 |
1991年 | 18017篇 |
1990年 | 17832篇 |
1989年 | 17224篇 |
1988年 | 16021篇 |
1987年 | 15160篇 |
1986年 | 14076篇 |
1985年 | 14140篇 |
1984年 | 11610篇 |
1983年 | 10004篇 |
1982年 | 7381篇 |
1981年 | 6735篇 |
1980年 | 6289篇 |
1979年 | 10808篇 |
1978年 | 8607篇 |
1977年 | 7756篇 |
1976年 | 7394篇 |
1975年 | 8559篇 |
1974年 | 9255篇 |
1973年 | 9098篇 |
1972年 | 8088篇 |
1971年 | 7521篇 |
1970年 | 6460篇 |
1969年 | 6187篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
G. Andreatta L. Deserti L. N. Giraldo 《Flexible Services and Manufacturing Journal》1995,7(3):207-227
The flexible manufacturing system (FMS) considered in this paper is composed of two CNC machines working in series—a punching machine and a bending machine connected through rollers acting as a buffer system of finite capacity. The main difference between the present problem and the standard two-machine flow shop problem with finite intermediate capacity is precisely the buffer system, which in our problem consists of two stacks of parts supported by rollers: the first stack contains the output of the punching machine, while the second stack contains the input for the bending machine. When the second stack is empty, the first stack may be moved over. Furthermore, the capacity of each stack depends on the particular part type being processed. The FMS can manufacture a wide range of parts of different types. Processing times on the two machines are usually different so that an unbalance results in their total workload. Furthermore, whenever there is a change of the part type in production, the machines must be properly reset—that is, some tools need to be changed or repositioned. A second important difference between the present problem and the usual two-machine flow shop problem is the objective. Given a list ofp part types to be produced in known quantities, the problem considered here is how to sequence or alternate the production of the required part types so as to achieve various hierarchical targets: minimize the makespan (the total time needed to complete production) and, for instance, compress the idle periods of the machine with less workload into a few long enough intervals that could be utilized for maintenance or other reasons. Although Johnson's rule is optimal in some particular cases, the problem addressed in the paper isNP-hard in general: heuristic procedures are therefore provided. 相似文献
53.
54.
55.
56.
The antimicrobial activity of cryptolepine is influenced by the type of medium employed, agitation and the presence of non-inhibitory concentrations of EDTA. The use of Mueller–Hinton broth (MHB), iso-sensitest broth and tryptone soya broth (TSB) produced lower minimum inhibitory concentrations (MICs) for some of the test organisms compared with nutrient broth or yeast dextrose broth (YDB). For example, a fourfold drop in MIC was recorded for Saccharomyces cerevisiae in MHB compared with the same organism tested in YDB. Agitation of the broths during incubation nearly always produced lower MICs for the bacteria, an eightfold decrease in MIC being recorded for Escherichia coli cultured in nutrient broth with agitation compared with a statically maintained culture. A non-inhibitory concentration (10−3 mol l−1 ) of disodium EDTA enhanced the antimicrobial activity of cryptolepine. Against E. coli NCTC 11560, an eightfold decrease in MIC and minimum bactericidal concentration (MBC) was recorded when tested in the presence of EDTA. 相似文献
57.
Norma L. Pucheu Norma L. Kerber Emilio A. Rivas Néstor Cortez Augusto F. Garcia 《Current microbiology》1997,34(3):155-161
Membranes from in vivo labeled cells of Rhodobacter
capsulatus U43[pTX35] grown photosynthetically carried 60% of
the [32P]-Pi in the “heavy” fraction (HM) after
sucrose gradient sedimentation. Metal-chelating chromatography of either
“heavy” or “light” (LM) membrane fractions rendered
similar Bchl-protein complex profiles after octyl-glucoside treatment,
including most of the radioactivity in the same corresponding elution
fraction (F II). Similar labeling distribution of pigment-protein complexes
was obtained for membranes of dark-grown cells induced by lowering oxygen
tension. Fractions derived from HM showed highly labeled LHIα, whereas the
same complex from LM was essentially [32P]-Pi-free, as revealed
by SDS-PAGE followed by autoradiography. Phospholipid analysis showed a
similar pattern for membranes isolated from cells photosynthetically or
semiaerobically grown, being the most abundant: phosphatidylglycerol,
phosphatidylethanolamine, cardiolipin, and phosphatidylcholine. Part of the
phospholipids from HM comigrated with LHIα during SDS-PAGE and dissociated
from the complexes only after solvent extraction and hydrophobic
chromatography. However, a small amount remained always attached to LHIα,
indicating an unusual strong interaction. These results suggest the existence
of two operationally defined membrane regions carrying LHIα complexes
differing in phosphorylation status and protein-phospholipid interaction.
Received: 10 August 1996 / Accepted: 10 September 1996 相似文献
58.
59.
Counts of Steller sea lion ( Eumetopias jubatus ) pups and non-pups (adults and juveniles) from aerial photographs of rookeries at Año Nuevo Island between 1990 and 1993 were significantly higher than those made on the ground. Based on regression of natural logs of photographic counts versus year, the number of pups declined at a rate of −0.099yr while non-pup numbers declined at −0.315/yr. Examination of ground count data for the same period revealed a significant decline in non-pups (−0.139/yr), but no trend was detected in the ground counts of pups. The regression coefficients from photographic and ground counts of non-pups did not differ significantly. Power analyses using the program TRENDS indicated that detectable rates of change in abundance from four annual surveys were much lower for counts of pups than counts of non-pups where sampling precision was based on fits to linear models. 相似文献
60.