全文获取类型
收费全文 | 45301篇 |
免费 | 3712篇 |
国内免费 | 5440篇 |
专业分类
电工技术 | 2101篇 |
技术理论 | 66篇 |
综合类 | 5546篇 |
化学工业 | 5946篇 |
金属工艺 | 947篇 |
机械仪表 | 2554篇 |
建筑科学 | 15593篇 |
矿业工程 | 3055篇 |
能源动力 | 1237篇 |
轻工业 | 719篇 |
水利工程 | 1943篇 |
石油天然气 | 1038篇 |
武器工业 | 739篇 |
无线电 | 1980篇 |
一般工业技术 | 4097篇 |
冶金工业 | 1109篇 |
原子能技术 | 142篇 |
自动化技术 | 5641篇 |
出版年
2024年 | 70篇 |
2023年 | 652篇 |
2022年 | 801篇 |
2021年 | 1254篇 |
2020年 | 1343篇 |
2019年 | 1008篇 |
2018年 | 968篇 |
2017年 | 1171篇 |
2016年 | 1443篇 |
2015年 | 1552篇 |
2014年 | 3935篇 |
2013年 | 2723篇 |
2012年 | 3275篇 |
2011年 | 3550篇 |
2010年 | 2969篇 |
2009年 | 3059篇 |
2008年 | 3033篇 |
2007年 | 3679篇 |
2006年 | 3362篇 |
2005年 | 3023篇 |
2004年 | 2660篇 |
2003年 | 2034篇 |
2002年 | 1452篇 |
2001年 | 1101篇 |
2000年 | 912篇 |
1999年 | 750篇 |
1998年 | 497篇 |
1997年 | 425篇 |
1996年 | 366篇 |
1995年 | 304篇 |
1994年 | 233篇 |
1993年 | 203篇 |
1992年 | 163篇 |
1991年 | 90篇 |
1990年 | 67篇 |
1989年 | 55篇 |
1988年 | 43篇 |
1987年 | 28篇 |
1986年 | 19篇 |
1985年 | 24篇 |
1984年 | 32篇 |
1983年 | 21篇 |
1982年 | 15篇 |
1981年 | 10篇 |
1980年 | 16篇 |
1979年 | 9篇 |
1961年 | 4篇 |
1958年 | 4篇 |
1957年 | 6篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
根据翼城上河煤矿岩层的实际情况,采用工程类比法确定了巷道支护参数,并对巷道的支护参数进行了校核,以保证巷道支护的有效性。重点分析了矩形巷道断面和半圆拱形断面巷道的支护参数设计,以期为类似支护提供一定的参考。 相似文献
72.
Jiwon Lee Bryan S. Der Christos S. Karamitros Wenzong Li Nicholas M. Marshall Oana I. Lungu Aleksandr E. Miklos Jianqing Xu Tae Hyun Kang Chang-Han Lee Bing Tan Randall A. Hughes Sang Taek Jung Gregory C. Ippolito Jeffrey J. Gray Yan Zhang Brian Kuhlman George Georgiou Andrew D. Ellington 《American Institute of Chemical Engineers》2020,66(3):e16864
We used the molecular modeling program Rosetta to identify clusters of amino acid substitutions in antibody fragments (scFvs and scAbs) that improve global protein stability and resistance to thermal deactivation. Using this methodology, we increased the melting temperature (Tm) and resistance to heat treatment of an antibody fragment that binds to the Clostridium botulinum hemagglutinin protein (anti-HA33). Two designed antibody fragment variants with two amino acid replacement clusters, designed to stabilize local regions, were shown to have both higher Tm compared to the parental scFv and importantly to retain full antigen binding activity after 2 hr of incubation at 70°C. The crystal structure of one thermostabilized scFv variants was solved at 1.6 Å and shown to be in close agreement with the RosettaAntibody model prediction. 相似文献
73.
以不同硅烷偶联剂改性的介孔分子筛SBA-15为载体、PW_(12)为催化剂,通过对SBA-15表面共价及非共价修饰制备磷钨酸@介孔分子筛/硅烷偶联剂复合催化剂PW_(12)@SBA-15/YSiX_3(YSiX_3=Apts、Atapts、Papts);并利用FT-IR、XRD、TEM、N_2吸附-脱附对其组成、结构及形貌进行表征。以改性SBA-15分子筛固载磷钨酸催化剂催化合成叔丁基苯酚为研究对象,考察不同硅烷偶联剂、反应温度、苯酚与叔丁醇物质的量比对催化合成叔丁基苯酚的影响,并获得合成叔丁基苯酚的最佳工艺条件,即反应温度145℃、n(苯酚)∶n(叔丁醇)=1∶2.5、重时空速2.2 h~(-1),该最佳反应条件下,PW_(12)@SBA-15/Apts催化剂催化合成叔丁基苯酚的催化活性最高,苯酚转化率为98.3%,2,4-二叔丁基苯酚选择性为57.3%. 相似文献
74.
Dr. Manuel Nieto-Domínguez Dr. Pablo I. Nikel 《Chembiochem : a European journal of chemical biology》2020,21(18):2551-2571
The diversity of life relies on a handful of chemical elements (carbon, oxygen, hydrogen, nitrogen, sulfur and phosphorus) as part of essential building blocks; some other atoms are needed to a lesser extent, but most of the remaining elements are excluded from biology. This circumstance limits the scope of biochemical reactions in extant metabolism – yet it offers a phenomenal playground for synthetic biology. Xenobiology aims to bring novel bricks to life that could be exploited for (xeno)metabolite synthesis. In particular, the assembly of novel pathways engineered to handle nonbiological elements (neometabolism) will broaden chemical space beyond the reach of natural evolution. In this review, xeno-elements that could be blended into nature's biosynthetic portfolio are discussed together with their physicochemical properties and tools and strategies to incorporate them into biochemistry. We argue that current bioproduction methods can be revolutionized by bridging xenobiology and neometabolism for the synthesis of new-to-nature molecules, such as organohalides. 相似文献
75.
76.
77.
C. Busuioc C.D. Ghitulica A. Stoica M. Stroescu G. Voicu V. Ionita L. Averous S.I. Jinga 《Ceramics International》2018,44(8):9433-9441
Bacterial cellulose membranes were employed as templates for calcium phosphates deposition by successive immersion in solutions of Ca(NO3)2·4H2O and (NH4)2HPO4, under ultrasonication. During the wet chemical reaction, mineral phases were loaded on bacterial cellulose fibrils, leading to precursor hybrid composites. These were subjected to a lyophilisation procedure in order to preserve the 3D porous aspect and afterwards to a thermal treatment with the aim of removing the polymeric phase and generating well crystallized structures. Different types of morphologies were achieved by varying the heating rate, as well as the calcination temperature and period. The as-prepared samples and the final ones were investigated from compositional and structural point of view through X-ray diffraction and Fourier-transform infrared spectroscopy and morphologically concerning by scanning electron microscopy. The magnetic properties were also evaluated in order to demonstrate the suitability of the obtained materials for the development of magnetic scaffolds dedicated to hard tissue applications. 相似文献
78.
Saba Mehrafzoon S.A. Hassanzadeh-Tabrizi Ashkan Bigham 《Ceramics International》2018,44(12):13951-13958
In this research, a bimodal nanoporous Baghdadite (NB) (Ca3ZrSi2O9) was prepared by a modified sol-gel method using P123 as a surfactant. The effects of P123's contents on the structural and textural properties as well as the drug delivery behavior of NB were assessed in vitro. The usage of P123 offered a new route for the synthesis of NB. The synthesized NB samples with different amounts of P123 were studied through X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), N2 adsorption-desorption, field emission scanning electron microscopy (FESEM) equipped with energy-dispersive X-ray analysis spectroscopy (EDAX) and transmission electron microscopy (TEM). The results showed that a single-phase Baghdadite was obtained by this new method at the calcination temperature of 800?°C. It was found that an increase in P123's content up to 0.025?mol changed the morphology of NB samples from mountain-like to needle-like. The potential application of NB samples as drug delivery agents was assessed by estimating their release properties up to 240?h. This research revealed that the synthesized Baghdadite could be used as a potential nanoporous carrier with controlled release capability in bone tissue regeneration. 相似文献
79.
80.