全文获取类型
收费全文 | 588297篇 |
免费 | 7545篇 |
国内免费 | 1859篇 |
专业分类
电工技术 | 10617篇 |
综合类 | 481篇 |
化学工业 | 89642篇 |
金属工艺 | 23369篇 |
机械仪表 | 17884篇 |
建筑科学 | 14847篇 |
矿业工程 | 2975篇 |
能源动力 | 14918篇 |
轻工业 | 53122篇 |
水利工程 | 5950篇 |
石油天然气 | 9448篇 |
武器工业 | 35篇 |
无线电 | 72092篇 |
一般工业技术 | 115304篇 |
冶金工业 | 104803篇 |
原子能技术 | 11654篇 |
自动化技术 | 50560篇 |
出版年
2021年 | 4530篇 |
2019年 | 4237篇 |
2018年 | 7180篇 |
2017年 | 7299篇 |
2016年 | 7809篇 |
2015年 | 5409篇 |
2014年 | 9014篇 |
2013年 | 26566篇 |
2012年 | 14944篇 |
2011年 | 20594篇 |
2010年 | 16164篇 |
2009年 | 18343篇 |
2008年 | 19291篇 |
2007年 | 19570篇 |
2006年 | 17274篇 |
2005年 | 16050篇 |
2004年 | 15262篇 |
2003年 | 14890篇 |
2002年 | 14398篇 |
2001年 | 14643篇 |
2000年 | 13612篇 |
1999年 | 14121篇 |
1998年 | 32269篇 |
1997年 | 23426篇 |
1996年 | 18375篇 |
1995年 | 14329篇 |
1994年 | 12705篇 |
1993年 | 12563篇 |
1992年 | 9621篇 |
1991年 | 9265篇 |
1990年 | 8853篇 |
1989年 | 8571篇 |
1988年 | 8334篇 |
1987年 | 7107篇 |
1986年 | 7113篇 |
1985年 | 8465篇 |
1984年 | 7959篇 |
1983年 | 7079篇 |
1982年 | 6541篇 |
1981年 | 6459篇 |
1980年 | 6312篇 |
1979年 | 6212篇 |
1978年 | 5937篇 |
1977年 | 6818篇 |
1976年 | 8706篇 |
1975年 | 5135篇 |
1974年 | 4906篇 |
1973年 | 4898篇 |
1972年 | 4127篇 |
1971年 | 3645篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
81.
82.
83.
The study presents a hypothesis on how randomness could be simulated by human subjects. Three sources of deviation from randomness are predicted: (1) the preferred application of overlearned production schemata for producing sequences of digits, (2) a wrong concept of randomness, and (3) the impossibility to monitor for redundancies of higher- than those of first-order. Deviations of random generation of digits produced by healthy subjects, patients with chronic frontal lobe damage, and patients with Parkinson's disease from random sequences produced by a computer program can be explained by the differential influence of these factors. Whereas incorrect concepts of randomness and limits on monitoring capacity distinguished all sequences produced by humans from actual random sequences, persistence on a single production strategy distinguished brain-damaged patients from controls. Random generation of digits appears to be a theoretically transparent and clinically useful test of executive function. 相似文献
84.
85.
Robben J.; der Schueren J.Van; Verhasselt P.; Aert R.; Volckaert G. 《Protein engineering, design & selection : PEDS》1995,8(2):159-165
The deletion of nine residues from the C-terminus of the bacterialchloramphenicol acetyltransferase (CAT) results in depositionof the mutant protein in cytoplasmic inclusion bodies and lossof chloramphenicol resistance in Escherichia coli. This foldingdefect is relieved by C-terminal fusion of the polypeptide withas few as two residues. Based on these observations, efficientpositive selection for the cloning of DNA fragments has beendemonstrated. The cloning vector encodes a C-terminally truncatedCAT protein. Restriction sites in front of the stop codon allowthe insertion of target DNA, resulting in the production ofproperly folded CAT fusion proteins and regained chloramphenicolresistance. The positive selection of recombinants is accomplishedby growth of transformants on chloramphenicol-containing agarplates. The method appears particularly convenient for the cloningof DNA fragments amplified by the PCR because minimal informationto restore CAT folding can be included in the primers. The cloningof random sequences shows that the folding defect can be relievedby fusion to a wide variety of peptides, providing great flexibilityto the positive selection system. This vector may also contributeto the determination of the role of the C-terminus in CAT folding. 相似文献
86.
Several in vivo and in vitro methods for monitoring immunological properties of two allergoids obtained by formaldehyde treatment of ovalbumin (OA) were developed. The calculated molecular weight of allergoids was 80 kD (OA-F1) and 165 kD (OA-F2), respectively. The allergenic activity in vitro of allergoids in mast-cell histamine release assay was 1000 times lower than of OA. Both allergoids showed reduced ability to induce passive cutaneous anaphylaxis in the Sprague-Dawley rats or systemic anaphylaxis in Dunkin-Harley guinea-pigs. The ability of OA and allergoids to bind to the OA-specific IgE antibodies was measured in vivo by the inhibition of passive cutaneous anaphylaxis (PCA-inhibition). Allergoid binding to IgE was 51-66% lower than the native allergen. Moreover, the avidity of OA-specific IgG antibodies, measured by ELISA-inhibition, for allergoids and allergen was of the same order. Allergoids induced a different pattern of humoral immune response from that, induced by the native allergen. Thus, after immunization of BALB/c mouse, both allergoids induced a higher production of IgG and a lower production of IgE than OA, only OA-F2 induced a lower production of IgG1. The differences in the IgA response to the immunogens was not significant. Delayed hypersensitivity studies in the BALB/c mouse showed that allergoids were 5- to 12-times less effective in inducing a cell-mediated immune response than OA. The present study provides a battery of immunological methods for preclinical testing of modified allergens. 相似文献
87.
This paper presents a model of heterogenous diffusion in capillary porous materials during the process of drying. The governing heat and mass transfer equations have been established using the liquid as well as vapor flow. Two models have been presented. Model 1 does not consider the heat conduction while the model 2 has been established by considering the conduction. The developed models and the numerical solutions of the resulting differential equations can take into account the moisture and temperature dependent thermophysical properties of the product. All equations have been established in spherical coordinates but the programme written for the purpose of calculations can be used for other geometries also. Numerical calculations have been performed for gas concrete and tiles using model 1, while model 2 has been used for gas concrete only because of the lack of data for thermophysical properties of the tile. For gas concrete it was seen that conduction has only marginal effect on the drying process and the numerical predictions of the drying process were reasonably accurate. 相似文献
88.
α,ω-Methacrylate-terminated poly(1,3-dioxolane)s (polyDXL) were synthesized by cationic ring-opening polymerization of DXL in the presence of methylene-bis(oxyethylmethacrylate) as transfer agent. If the initiator concentration is small compared with the transfer agent concentration, the molecular weights of the polymers are governed by the ratio of the reacted monomer to the reacted transfer agent. The α,ω-methacrylate-terminated polyDXLs obtained undergo free radical polymerization with formation of polyacetal networks. The properties of the networks as function of the molecular weight of the corresponding prepolymers are reported. 相似文献
89.
Muralidhar N. Ingale Vijaykumar V. Mahajani 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1995,64(1):80-86
The effectiveness of the hybrid system sonication followed by wet oxidation (SONIWO) to treat otherwise refractory waste has been demonstrated. In such a hybrid system homogeneous CuSO4 catalyst was found to be very efficient. 相似文献
90.
V. A. Arzamastsev N. L. Sardaev A. S. Kochergin 《Metal Science and Heat Treatment》1996,38(11):477-479
The technological process of cold forging applied for the first time in the production of the casing of the internal joint with races is described. The process operations of cold forging and the annealing and carburizing regimes for this part me described. 相似文献