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31.
The effect of miscible low molecular weight additives on the mobility of the carbonate group in bisphenol-A polycarbonate (BPAPC) has been studied using n.m.r. and dielectric relaxation experiments in the solid state. Proton-enhanced dipolar-decoupled carbon-13 n.m.r. spectra of BPAPC, isotopically enriched at the carbonate position, are obtained without magic-angle sample spinning. The resolved chemical shift anisotropy allows study of nuclear spin relaxation for the carbonate groups in the polymer that have different orientations relative to the static magnetic field in the laboratory frame. The spin-lattice relaxation time in the rotating frame (m>T m>1m>? m>) is measured at a motional-probe frequency of 50 kHz for the undiluted polymer and for BPAPC-diluent blends containing either dibutylphthalate or dinitrobiphenyl. The m>T m>1m>? m> exhibits some dependence on orientation in all systems studied. In the blend containing dibutylphthalate (DBP), m>T m>1m>? m> is decreased by a factor of two for all orientations of the carbonate group. This implies that DBP substantially increases the spectral density of 50 kHz motions in the carbonate region of the polymer at ambient temperature. In contrast, dinitrobiphenyl does not significantly alter the Fourier component of thermal fluctuations at 50 kHz. Dielectric relaxation measurements at 10 kHz reveal that the primary (m>T m>g) and secondary (β) motional processes in BPAPC are affected by low molecular weight additives. An intermediate relaxation process appears in the temperature interval between the glass transition temperature (m>T m>g) and the sub-m>T m>g β-relaxation (m>T m>m>β m>) in the polymer-diluent blends. The n.m.r. spin-lattice relaxation rate in the rotating frame, m>T m>?11m>? m>, correlates well with the relative magnitude of the dielectric dissipation factor (tan m>δ m>m>ε m>) between m>T m>g and m>T m>m>β m>. 相似文献
32.
33.
Based on B-series theory, the order conditions of the multidimensional ARKN methods are presented for the general multi-frequency and multidimensional oscillatory second-order initial value problems by Wu et&nbsp;al. (2009). These multidimensional ARKN methods exactly integrate the multi-frequency and multidimensional unperturbed oscillators. In this paper, we pay attention to the analysis of the concrete multidimensional ARKN methods for the general multi-frequency oscillatory second-order initial value problems whose right-hand side functions m>depend on both &#xA0; m>y<math altimg="si3.gif" overflow="scroll"><mi>ymi>math>m>and &#xA0; m>y&prime;<math altimg="si4.gif" overflow="scroll"><msup><mrow><mi>ymi>mrow><mrow><mo>&prime;mo>mrow>msup>math> (the class of physical problems which fall within its scope is broader). Numerical experiments are carried out to show that the new multidimensional ARKN methods are more efficient compared with some well-known methods for dealing with the oscillatory problems in the scientific literature. 相似文献
34.
1H dipolar decoupled 13C n.m.r. experiments with the aid of the magic angle spinning technique have been used to determine the graft content and the isomer content of the polybutadiene grafts in a graft copolymer with isotactic polypropylene. 相似文献
35.
36.
介绍了新开发的大型聚氯乙烯生产设备——108m3PVC聚合釜,通过对其技术特性、结构特点及生产能力等的介绍,阐明了该釜又是一个适应我国PVC行业发展需求的新釜型。 相似文献
37.
Xiaobao Li Richard P. K. Wells Peter B. Wells Graham J. Hutchings 《Catalysis Letters》2003,89(3-4):163-167
The premodification of a 5 wt% Pt/mg src="/content/m51x787331t24l32/xxlarge947.gif" alt="gamma" align="MIDDLE" BORDER="0">-Al2O3 catalyst with cinchonidine (0.01 and 0.2 g g-1
catalyst) is described and discussed. Premodification is carried out by treating the catalyst with a solution of cinchonidine followed by solvent removal. Catalysts premodified in this way give the same ee and initial rate of reaction for the enantioselective hydrogenation of ethyl pyruvate as those using the standard in situ modification procedure. Investigations of different solvents for premodification and reaction (dichloromethane, ethanol) show that it is the solvent used for the reaction that controls the observed enantioselection. Premodified catalysts also display the initial transient behavior typically observed with in situ modified catalysts in which the ee increases with conversion in the early part of the reaction. Premodified catalysts show an enhanced rate of reaction when ethanol is used as the reaction solvent compared with in situ modified catalysts under the same conditions. Premodification using aerobic conditions gives the best results and premodified catalysts can be stored prior to use for up to a week without loss of catalytic performance. 相似文献
38.
锂离子电池炭负极材料研究现状与发展 总被引:1,自引:0,他引:1
综述了近年来各种炭材料作为锂离子电池负极材料的新进展,着重分析了石墨、焦炭和难石墨化炭在放电容量、不可逆容量损失、充放电电位和充放电速率等主要性能上的差异以及与其结构之间的联系;指出以PAS为代表的热解炭(低于800℃)和纳米炭材料将是锂离子电池负极材料的发展方向。 相似文献
39.
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
40.
Ni&#x2013;W catalysts were prepared by impregnation of commercial mg src="/content/g0805166532221m8/xxlarge947.gif" alt="gamma" align="MIDDLE" BORDER="0">-alumina and silica supports. The sulfidation, performed directly after drying at 100&deg;C, yielded fully sulfided Ni&#x2013;W species on both supports (SEM-EDAX, XPS, XRD). At optimal metals loading (mg src="/content/g0805166532221m8/xxlarge8764.gif" alt="sim" align="MIDDLE" BORDER="0">50 wt% NiO + WO3, Ni/W = 2), the sulfided catalysts had similar texture (N2 adsorption) and displayed similar activity in dibenzothiophene hydrodesulfurization (DBT HDS), while the activity of the Ni&#x2013;W/SiO2 catalyst in toluene hydrogenation (HYD) was six times higher than that of Ni&#x2013;W/Al2O3. This is due to the more than two times higher WS2 slabs stacking number in Ni&#x2013;W/SiO2 compared with Ni&#x2013;W/Al2O3 (XRD, HR-TEM), yielding stronger adsorption of toluene (TPD). 相似文献