全文获取类型
收费全文 | 16139篇 |
免费 | 1243篇 |
国内免费 | 854篇 |
专业分类
电工技术 | 861篇 |
综合类 | 1003篇 |
化学工业 | 2683篇 |
金属工艺 | 783篇 |
机械仪表 | 863篇 |
建筑科学 | 1372篇 |
矿业工程 | 411篇 |
能源动力 | 557篇 |
轻工业 | 1100篇 |
水利工程 | 203篇 |
石油天然气 | 712篇 |
武器工业 | 85篇 |
无线电 | 1725篇 |
一般工业技术 | 1802篇 |
冶金工业 | 1132篇 |
原子能技术 | 306篇 |
自动化技术 | 2638篇 |
出版年
2024年 | 88篇 |
2023年 | 280篇 |
2022年 | 439篇 |
2021年 | 589篇 |
2020年 | 474篇 |
2019年 | 380篇 |
2018年 | 436篇 |
2017年 | 498篇 |
2016年 | 430篇 |
2015年 | 594篇 |
2014年 | 752篇 |
2013年 | 989篇 |
2012年 | 886篇 |
2011年 | 1022篇 |
2010年 | 932篇 |
2009年 | 896篇 |
2008年 | 875篇 |
2007年 | 858篇 |
2006年 | 876篇 |
2005年 | 753篇 |
2004年 | 534篇 |
2003年 | 443篇 |
2002年 | 462篇 |
2001年 | 410篇 |
2000年 | 443篇 |
1999年 | 419篇 |
1998年 | 352篇 |
1997年 | 289篇 |
1996年 | 281篇 |
1995年 | 216篇 |
1994年 | 185篇 |
1993年 | 137篇 |
1992年 | 108篇 |
1991年 | 105篇 |
1990年 | 76篇 |
1989年 | 60篇 |
1988年 | 54篇 |
1987年 | 45篇 |
1986年 | 63篇 |
1985年 | 33篇 |
1984年 | 39篇 |
1983年 | 36篇 |
1982年 | 36篇 |
1981年 | 39篇 |
1980年 | 26篇 |
1979年 | 22篇 |
1978年 | 21篇 |
1977年 | 23篇 |
1976年 | 20篇 |
1975年 | 32篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
92.
本文研究了从发酵液中用D2EHPA-煤油溶剂萃取分离L-异亮氨酸工艺.考察了萃取时pH值、萃取剂浓度和异亮氨酸浓度对于异亮氨酸和缬氨酸的萃取分配比的影响.在计算机上进行回归,得到以下分配模型:当1≤pH≤3.5时lgDIle=0.09906pH2+0.8625pH+2.2696lgCHR-0.09188lg2CIle+0.1766lgCIle-1.366lgDrmVal=-0.0293pH2+0.550pH+1.2659lgCHR-0.2420lg2CIle+0.4549lgCIle-1.696用此模型,应用分馏萃取理论,进行逐级计算,求取了萃取工艺的主要参数,并在φ20mm的多级离心萃取器上对上述结果进行了验证.结果表明:当CHR浓度为1.5mol/L,相比V:L:L’=2:1:2,N’=3,N=6时,异亮氨酸的收率达到90%以上,纯度>99%.实验取得了较为满意的结果. 相似文献
93.
This paper presents a robotic head for social robots to attend to scene saliency with bio-inspired saccadic behaviors. Scene saliency is determined by measuring low-level static scene information, motion, and object prior knowledge. Towards the extracted saliency spots, the designed robotic head is able to turn gazes in a saccadic manner while obeying eye–head coordination laws with the proposed control scheme. The results of the simulation study and actual applications show the effectiveness of the proposed method in discovering of scene saliency and human-like head motion. The proposed techniques could possibly be applied to social robots to improve social sense and user experience in human–robot interaction. 相似文献
94.
种子法制备聚合物乳液技术的进展 总被引:2,自引:0,他引:2
从建筑乳液的生产现状、自生种子法与外加种子法的区别、种子乳液的特点及外加种子法生产的乳液特性等方面介绍了种子法制备乳液技术的进展。 相似文献
95.
以对氨基苯磺酸为起始原料 ,经过乙酰化、硝化、水解三步来制备标题物。通过正交试验找出了酰化的最佳反应条件为 :对氨基苯磺酸与乙酐的摩尔比为 1∶1.0 5 ,反应总时间为 1.5h ,反应温度为 2 5℃ ,酰化介质为酰化反应前用碳酸钠及水将对氨基苯磺酸完全溶解 ,使混合液 pH值为 5~ 6 ,反应过程中不再补加碳酸钠 ,其酰化转化率可达 99.6 % ,酰化产物的固体收率可达 96 .0 % ;硝化反应的最佳条件为 :硝化剂用 90 .2 %的硝酸 ,对乙酰氨基苯磺酸与硝化剂的摩尔比为 1∶1.0 5 ,反应温度为 10℃ ,浓硫酸与对乙酰氨基苯磺酸的摩尔比为 8.3∶1,其硝化转化率可达 96 .0 % ,硝化反应的选择性好 ,对氨基邻硝基苯磺酸的量不到 1.0 %。 相似文献
96.
Silphinene Sesquiterpenes as Model Insect Antifeedants 总被引:3,自引:0,他引:3
González-Coloma A Valencia F Martín N Hoffmann JJ Hutter L Marco JA Reina M 《Journal of chemical ecology》2002,28(1):117-129
Silphinene sesquiterpenes are established chrysomelid antifeedants. In this work, nine silphinene analogs, 11-acetoxy-5-angeloyloxysilphinen-3-one (1), 11-acetoxy-5-tigloyloxysilphinen-3-one (2), 11-acetoxy-5-iso- butyryloxysilphinen-3-one (3), 11-hydroxy-5-angeloyloxysilphinen-3-one (4), 11,5-dihydroxysilphinen-3-one (5), 11,5-diacetoxysilphinen-3-one (6), 5,11-diisobutyryloxysilphinen-3-one (7), silphinen-3,5,11-trione (8), and O-methyl-5-epicantabrenolic acid methyl ester (10), and a presilphiperfolane sesquiterpene (9) were tested against several divergent insect species, including the lepidopteran Spodoptera littoralis, the chrysomelid Leptinotarsa decemlineata, and five aphid species, and their antifeedant effects were compared with those of picrotoxinin, a GABA-antagonist, and thymol, an allosteric modulator for insect GABA receptors. All insects tested responded to at least one silphinene analog and/or GABA antagonist. Compound 3 and thymol were effective antifeedants against all species tested except S. littoralis, with varying potencies according to their feeding ecologies. The toxicity of these compounds was species-dependent and did not correlate with their antifeedant effect. 相似文献
97.
98.
Summary The herbicide 2,4-D was microencapsulated using ethyl cellulose to develop controlled release formulations that protect it from photodegradation and evaporation and to reduce the environment pollution. Ethyl cellulose microspheres loaded with 2,4-D were prepared by the emulsion solvent-evaporation technique. We have obtained the desired microspheres with higher drug entrapment and encapsulation yield by varying certain conditions as stirring speed, polymer-solvent ratio, drug-polymer ratio, pH of continuous phase and organic phase solvent. The shape and size of microspheres were analysed by scanning electron microscopy. The herbicide release was studied at 25 °C and the release data were analysed according to Fick’s Law. The results demonstrate that we can control the release rate by modifying the process parameters. 相似文献
99.
100.
Xiang Jim; Sha Yuhua; Prasad Lata; Delbaere Louis T.J. 《Protein engineering, design & selection : PEDS》1996,9(6):539-543
Structural analysis derived from the crystallographic studyof the chimeric B72.3 antibody illustrated some major atomicinteractions between complementarity determining region (CDR)residues. For example, hydrogen bonds are formed between H35/H95,L50/H97, H53/H55 and H96/L96 respectively. These CDR residuesmay play important roles in the B72.3TAG72 (antibody-antigen)interaction either by direct interaction with the TAG72 antigenor by maintaining a CDR loop conformation through atomic interactionsbetween CDR residues. In order to confirm these assumptions,we altered these CDR residues by site-directed mutagenesis anddetermined binding affinities of these mutant chimeric antibodiesfor the TAG72 antigen in a solid-phase radioimmunoassay. Wefound that H55, H95, H97 and L96 are important CDR residuesfor the B72.3TAG72 interaction. Single amino acid substitutionsof aspartic acid and serine by alanine at H55 of CDR2 and atH95 of CDR3 respectively and of tyrosine by phenylalanine atH97 and L96 of CDR3, significantly reduced the binding affinityfor the TAG72 antigen by 20-, 8-, 16- and 45-fold respectively.Therefore, this study reveals some of the requirements for maintainingthe integrity of the B72.3 antibody combining sites. 相似文献