全文获取类型
收费全文 | 3923篇 |
免费 | 81篇 |
国内免费 | 796篇 |
专业分类
电工技术 | 61篇 |
综合类 | 209篇 |
化学工业 | 245篇 |
金属工艺 | 938篇 |
机械仪表 | 249篇 |
建筑科学 | 28篇 |
矿业工程 | 60篇 |
能源动力 | 49篇 |
轻工业 | 169篇 |
水利工程 | 142篇 |
石油天然气 | 221篇 |
武器工业 | 7篇 |
无线电 | 285篇 |
一般工业技术 | 282篇 |
冶金工业 | 1306篇 |
原子能技术 | 32篇 |
自动化技术 | 517篇 |
出版年
2021年 | 4篇 |
2020年 | 7篇 |
2019年 | 9篇 |
2018年 | 4篇 |
2017年 | 19篇 |
2015年 | 11篇 |
2014年 | 33篇 |
2013年 | 50篇 |
2012年 | 51篇 |
2011年 | 976篇 |
2010年 | 436篇 |
2009年 | 184篇 |
2008年 | 143篇 |
2007年 | 70篇 |
2006年 | 141篇 |
2005年 | 117篇 |
2004年 | 330篇 |
2003年 | 198篇 |
2002年 | 153篇 |
2001年 | 119篇 |
2000年 | 56篇 |
1999年 | 139篇 |
1998年 | 478篇 |
1997年 | 290篇 |
1996年 | 170篇 |
1995年 | 80篇 |
1994年 | 70篇 |
1993年 | 123篇 |
1992年 | 46篇 |
1991年 | 20篇 |
1990年 | 16篇 |
1989年 | 24篇 |
1988年 | 13篇 |
1987年 | 13篇 |
1986年 | 12篇 |
1985年 | 11篇 |
1984年 | 4篇 |
1982年 | 12篇 |
1981年 | 10篇 |
1980年 | 7篇 |
1978年 | 4篇 |
1977年 | 38篇 |
1976年 | 78篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1970年 | 3篇 |
1969年 | 2篇 |
1885年 | 4篇 |
排序方式: 共有4800条查询结果,搜索用时 703 毫秒
1.
反转构造的反转程度及其与油气聚集的关系 总被引:10,自引:2,他引:8
结合典型反转构造地震剖面,分析了断层型和褶皱型两类反转构造的反转程度,上下皆正断层型和向形褶皱型反转构造的反转程度轻微;上逆下正断层型和透镜形褶皱型反转构造的反转程度中等;上下皆逆断层型和背形褶皱型反转构造的反转程度强烈。分析了反转构造的反转程度与油气聚集的关系,处于轻微反转程度的上下皆正断层型反转和向形褶皱型反转,以及处于强烈反转程度的上下皆逆断层型反转和背形褶皱型反转不利于油气聚集;处于中等反转程度的上逆下正断层型反转和透镜形褶皱型反转类型有利于油气聚集成藏。 相似文献
2.
本文将空间结构变化的要求与动态资料确定的储量共同作为约束,建立了包含两个约束条件的目标函数, 应用模拟退火算法对孔隙率的空间分布进行预测。在实现过程中,通过初始控制参数的给定及目标函数修改提高了运算效率。由于目标函数有效地整合了静、动态信息,从而降低了模拟结果的不确定性.提高了模拟的精度。合成数据及实际数据的模拟试验表明,整合区域特性约束不仅提高了孔隙率模拟精度,而且算法收敛快、稳定性高。 相似文献
3.
光学材料的激光微加工研究进展与应用前景 总被引:2,自引:1,他引:1
综述了国内外在光学材料激光微加工方面的研究成果和应用状况,并展望了其发展前景。 相似文献
4.
FT-Raman spectroscopy proves to be a powerful technique to study surface reactions on bioactive glasses and it eliminates the fluorescence of the organic phase of whole bone, thereby making it possible to compare the reaction layers formed on bioactive glasses with the mineral phase of bone. The spectrum of hydroxycarbonate apatite (HCA) developed on the bioactive glasses is closer to that of bone than synthetic hydroxyapatite (HA) and closely matches that of bone mineral obtained by deproteination of whole human femoral cortical bone. 相似文献
5.
Pax genes are expressed in specific patterns in the nervous system during development and in the adult. Recent findings suggest a link between the expression of Pax-2 and axonal guidance. Mice with a targeted deletion of Pax-2 are an excellent tool for studying axonal pathfinding at the molecular level, especially with respect to the optic chiasm. The date reviewed here suggest that Pax-2 regulates the expression of surface molecules involved in contact attraction and that the mutual regulation of the expression of Pax-2 and the Sonic hedgehog gene is of importance in the formation of the chiasm region. 相似文献
6.
Wenlin HE Qishan ZANG+ Zhongguang WANG State Key Laboratory for Fatigue Fracture of Materials 《材料科学技术学报》1993,9(2):107-110
The distributions of plastic strain near grain boundaries induced by fatigue loading were investigatedby the fiducial grid method in pure aluminum specimens, and the resulted grain boundary sliding(GBS) was systematically analysed. The results show that the strain field near a grain boundary isnonuniform. GBS is restricted by the junction of grain boundaries and causes discontinuities of bothdisplacement and strain. A peak value of shear strain was created in short-range area across the grainboundary. GBS plays an important role in cyclic softening and secondary hardening. The control fac-tor of GBS is the relative orientation between two grains and the macro orientation of the grainboundary rather than the ∑ value of the boundary. 相似文献
7.
LL McCabe 《Canadian Metallurgical Quarterly》1998,152(9):839-842
Agrobacterium tumefaciens transfers part of its Ti plasmid, the T-DNA, to plant cells during tumorigenesis. It is routinely used for the genetic modification of a wide range of plant species. We report that A. tumefaciens can also transfer its T-DNA efficiently to the filamentous fungus Aspergillus awamori, demonstrating DNA transfer between a prokaryote and a filamentous fungus. We transformed both protoplasts and conidia with frequencies that were improved up to 600-fold as compared with conventional techniques for transformation of A. awamori protoplasts. The majority of the A. awamori transformants contained a single T-DNA copy randomly integrated at a chromosomal locus. The T-DNA integrated into the A. awamori genome in a manner similar to that described for plants. We also transformed a variety of other filamentous fungi, including Aspergillus niger, Fusarium venenatum, Trichoderma reesei, Colletotrichum gloeosporioides, Neurospora crassa, and the mushroom Agaricus bisporus, demonstrating that transformation using A. tumefaciens is generally applicable to filamentous fungi. 相似文献
8.
We have shown that normal and human papillomavirus (HPV) type 16 immortalized human foreskin keratinocytes are growth inhibited by tumor necrosis factor alpha (TNF-alpha), whereas HPV-18- and SV40-immortalized keratinocytes are resistant to this cytokine (1). In this report, we investigated the expression of mitotic regulatory proteins, such as cyclin A, cyclin B, and p34cdc2. After exposure to TNF-alpha, normal and HPV-16-immortalized cells exhibited a dramatic decrease in the expression of these proteins. In contrast, no alteration in the levels of these proteins was observed after treatment of the resistant cell lines, as well as two HPV-positive cervical carcinoma cell lines. Expression of cyclin E does not seem to be modulated by TNF-alpha in any of the cells tested. On the other hand, cyclin D1, expression is slightly increased in normal keratinocytes and in the HPV-16-immortalized cells, whereas no alteration was observed in the HPV-18-transfected cells. The phosphorylation state of pRb correlated with cell growth; sensitive cells, which accumulate in G0-G1, after exposure to TNF-alpha, exhibited an accumulation of hypophosphorylated pRb, whereas no effect on pRb phosphorylation was observed for HPV-18-immortalized cells. These results clearly correlate with TNF-alpha-induced growth arrest in G0-G1. 相似文献
9.
10.
JT Queenan LL Veeck JP Toner S Oehninger SJ Muasher 《Canadian Metallurgical Quarterly》1997,12(7):1573-1576
In-vitro fertilization patients (n = 15) at risk of ovarian hyperstimulation syndrome (OHSS) (oestradiol > or =4500 pg/ml on the day of human chorionic gonadotrophin administration and 25 or more follicles of intermediate or large size) underwent aspiration of all follicles and cryopreservation of all fertilized oocytes at the pronuclear stage. Patients were monitored for up to 2 weeks post-retrieval. Subsequent transfer of cryopreserved-thawed embryos was performed in programmed cycles using exogenous oestrogen and progesterone for endometrial preparation. Two patients (13%) developed OHSS necessitating hospitalization and vaginal aspiration of ascitic fluid. Two other patients (13%) developed moderate OHSS requiring ascitic fluid vaginal aspiration in the office setting, with dramatic improvement of the condition. Subsequent transfer of cryopreserved-thawed embryos yielded a clinical pregnancy rate of 58% per transfer and ongoing or delivery rates of 42 and 67% per transfer and per patient respectively. By eliminating pregnancy potential with cryopreservation of all prezygotes and examining the pregnancy potential with subsequent cryopreserved-thawed transfers, it is concluded that OHSS is reduced, but not eliminated for patients at risk. Subsequent transfer of cryopreserved-thawed prezygotes in a programmed cycle with exogenous steroids yields an excellent pregnancy rate. 相似文献