全文获取类型
收费全文 | 73667篇 |
免费 | 5414篇 |
国内免费 | 2791篇 |
专业分类
电工技术 | 3901篇 |
技术理论 | 7篇 |
综合类 | 4439篇 |
化学工业 | 12711篇 |
金属工艺 | 3960篇 |
机械仪表 | 4808篇 |
建筑科学 | 5202篇 |
矿业工程 | 2410篇 |
能源动力 | 2238篇 |
轻工业 | 4791篇 |
水利工程 | 1002篇 |
石油天然气 | 5298篇 |
武器工业 | 470篇 |
无线电 | 7669篇 |
一般工业技术 | 9469篇 |
冶金工业 | 3937篇 |
原子能技术 | 760篇 |
自动化技术 | 8800篇 |
出版年
2024年 | 304篇 |
2023年 | 1269篇 |
2022年 | 2113篇 |
2021年 | 2926篇 |
2020年 | 2213篇 |
2019年 | 1972篇 |
2018年 | 2302篇 |
2017年 | 2510篇 |
2016年 | 2087篇 |
2015年 | 2706篇 |
2014年 | 3449篇 |
2013年 | 4233篇 |
2012年 | 4362篇 |
2011年 | 4871篇 |
2010年 | 4183篇 |
2009年 | 3964篇 |
2008年 | 3857篇 |
2007年 | 3718篇 |
2006年 | 3797篇 |
2005年 | 3434篇 |
2004年 | 2286篇 |
2003年 | 2085篇 |
2002年 | 1870篇 |
2001年 | 1639篇 |
2000年 | 1801篇 |
1999年 | 2048篇 |
1998年 | 1769篇 |
1997年 | 1426篇 |
1996年 | 1406篇 |
1995年 | 1186篇 |
1994年 | 958篇 |
1993年 | 717篇 |
1992年 | 547篇 |
1991年 | 428篇 |
1990年 | 327篇 |
1989年 | 254篇 |
1988年 | 226篇 |
1987年 | 142篇 |
1986年 | 120篇 |
1985年 | 96篇 |
1984年 | 66篇 |
1983年 | 40篇 |
1982年 | 42篇 |
1981年 | 30篇 |
1980年 | 25篇 |
1979年 | 13篇 |
1977年 | 7篇 |
1976年 | 8篇 |
1975年 | 5篇 |
1945年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
SW Qian JK Burmester PD Sun A Huang DJ Ohlsen L Suardet KC Flanders D Davies AB Roberts MB Sporn 《Canadian Metallurgical Quarterly》1994,33(40):12298-12304
Transforming growth factor-beta (TGF-beta) is a potent regulator of cell growth and differentiation. On the basis of the crystal structure of TGF-beta 2, we have designed and synthesized two mutant TGF-beta s, TGF-beta 1 (71 Trp) and TGF-beta 1 (delta 69-73). Although both of these molecules inhibited the growth of Mv1Lu mink lung epithelial cells and LS1034 colorectal cancer cells, which are affected equally by TGF-beta 1 and TGF-beta 2, TGF-beta 1 (delta 69-73) was much less potent than TGF-beta 1 or TGF-beta 1 (71 Trp) at inhibiting the growth of LS513 colorectal cancer cells which are growth-inhibited by TGF-beta 1 but not TGF-beta 2. Both TGF-beta 1 (71 Trp) and TGF-beta 1 (delta 69-73) increased levels of mRNAs for fibronectin and plasminogen activator inhibitor with Mv1Lu cells, whereas only TGF-beta 1 (71 Trp) and not TGF-beta 1 (delta 69-73) up-regulated the mRNA level of carcinoembryonic antigen in LS513 cells. The expression level of carcinoembryonic antigen mRNA in LS1034 cells was not altered by either wild-type or mutant TGF-beta s. Receptor labeling experiments demonstrated that TGF-beta 1 (71 Trp) bound with high affinity to the cell-surface receptors of Mv1Lu, LS1034, and LS513 cells while TGF-beta 1 (delta 69-73) bound effectively to the receptors of Mv1Lu and LS1034 cells but much less to the receptors on LS513 cells.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
42.
BaTiO3 multilayer capacitors with a nominal capacitance of 3.5nF have been carefully measured using the thermally stimulated current (TSC) technique. When a 300V polarization voltage is applied at room temperature, a new TSC peak appeared in defective sample A after it has been immersed in water. No new peak was found in good-quality sample B after a similar treatment. The accelerated life test shows that sample A hasa much shorter life than sample B in terms of insulation resistance. 相似文献
43.
44.
山洪灾害预警准确度与及时度研究 总被引:1,自引:0,他引:1
山洪灾害预警准确度与及时度是一对相互矛盾而又联系的重要指标。文章通过对这两项指标的研究和对引发灾害的降雨强度、降雨以及灾害发生的时间资料进行分析,从而获取预警系统建设的基本技术要点和参数,对把握山洪灾害预警系统的设计定位、启用时机和作用评估具有重要作用和意义。 相似文献
45.
In this work, we present three different formulations, namely the pressure field integral equation formulation (PFIE), the velocity field integral equation formulation (VFIE), and the combined field integral equation formulation (CFIE) for solving acoustic scattering problems associated with two-dimensional fluid-filled bodies of arbitrary cross-section. In particular using the boundary conditions on the surface of the body, two equivalent problems, each valid for the outside and inside regions of the scatterer, are derived. By properly selecting the associated equations for these equivalent problems, the three different formulations are derived. The PFIE, VFIE, and CFIE are then solved by approximating the cylindrical cross-section by linear segments and employing the method of moments. Further, it is shown that the moment matrices generated by the PFIE and VFIE are ill-conditioned at resonant frequencies of the cylinder, whereas the CFIE generates a well-conditioned matrix at all frequencies. The solution techniques presented in this work are simple, efficient and applicable to truly arbitrary geometries. Numerical results are presented for certain canonical shapes and compared with other available data. 相似文献
46.
报道了以茈为荧光探针,探讨小剂量~(60)Co γ射线照射后小鼠胸腺细胞膜流动性的变化。结果表明,剂量在0.25-1.00Gy范围,胸腺细胞膜流动性降低与剂量之间呈明显线性关系。从0.50Gy起,辐照组荧光强度比值I_1/I_2与I_3/I_2与对照组的比较存有显著差异(P<0.05)。提示淋巴细胞膜流动性的变化可作为小剂量辐照早期效应的敏感指标。 相似文献
47.
In CFD simulation of diesel combustion, the predictive capabilities of the spray model play the most important role. Consequently, under the strict guidelines of the V&V, a method to adjust parameters of diesel spray model WAVE to accompany with the in-cylinder physical progress has been investigated in this paper. Moreover, the simulation of the spray has been validated by high-speed photography experiments and verified by the equation proposed by Hiroyasu. Finally, a modified setup for the WAVE spray model has been proposed and applied in the spray and combustion simulation for Deutz1013 diesel in different engine speed. 相似文献
48.
49.
A novel fully conjugated polymer containing 1,10‐phenanthroline (DAPcDOD) was first synthesized by the polycondensation of 2,7‐dimethyl‐2,4,6‐octatriene‐1,8‐dial with 5,6‐diamine‐1,10‐phenanthroline. Three polymeric complexes were first prepared by the reaction of DAPcDOD with NiSO4, CoCl2, and FeSO4, respectively. The structures of the polymer and the complexes were characterized by IR, 1H‐NMR, and elemental analysis. The magnetic behaviors of these complexes were measured as a function of magnetic field strength (0–50 kOe) at 5 K and as a function of temperature (5–300 K) at a magnetic field strength of 30 kOe. The results show that DAPcDOD–Ni2+ and DAPcDOD–Co2+ were soft ferromagnets, whereas DAPcDOD–Fe2+ exhibited the features of an antiferromagnet. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
50.
通过对铸造湿型小件产品缺陷典型实例的原因分析,从型砂的选择及配制、造型工艺、浇注工艺等方面提出控制缺陷产生的工艺方法。 相似文献