全文获取类型
收费全文 | 83886篇 |
免费 | 1522篇 |
国内免费 | 965篇 |
专业分类
电工技术 | 1257篇 |
综合类 | 680篇 |
化学工业 | 10821篇 |
金属工艺 | 3649篇 |
机械仪表 | 2236篇 |
建筑科学 | 1679篇 |
矿业工程 | 540篇 |
能源动力 | 1813篇 |
轻工业 | 4260篇 |
水利工程 | 960篇 |
石油天然气 | 1434篇 |
武器工业 | 4篇 |
无线电 | 5784篇 |
一般工业技术 | 13966篇 |
冶金工业 | 28020篇 |
原子能技术 | 963篇 |
自动化技术 | 8307篇 |
出版年
2022年 | 329篇 |
2021年 | 443篇 |
2019年 | 420篇 |
2018年 | 1110篇 |
2017年 | 1326篇 |
2016年 | 1786篇 |
2015年 | 1309篇 |
2014年 | 1223篇 |
2013年 | 2781篇 |
2012年 | 3500篇 |
2011年 | 4261篇 |
2010年 | 2137篇 |
2009年 | 2514篇 |
2008年 | 2206篇 |
2007年 | 2373篇 |
2006年 | 1939篇 |
2005年 | 4540篇 |
2004年 | 3714篇 |
2003年 | 3100篇 |
2002年 | 1896篇 |
2001年 | 1845篇 |
2000年 | 1234篇 |
1999年 | 1603篇 |
1998年 | 8100篇 |
1997年 | 5315篇 |
1996年 | 3857篇 |
1995年 | 2385篇 |
1994年 | 1806篇 |
1993年 | 1842篇 |
1992年 | 833篇 |
1991年 | 873篇 |
1990年 | 820篇 |
1989年 | 755篇 |
1988年 | 657篇 |
1987年 | 619篇 |
1986年 | 557篇 |
1985年 | 544篇 |
1984年 | 373篇 |
1983年 | 378篇 |
1982年 | 422篇 |
1981年 | 464篇 |
1980年 | 530篇 |
1979年 | 401篇 |
1978年 | 390篇 |
1977年 | 1010篇 |
1976年 | 1900篇 |
1975年 | 404篇 |
1974年 | 332篇 |
1973年 | 356篇 |
1972年 | 315篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
J DiRuggiero N Santangelo Z Nackerdien J Ravel FT Robb 《Canadian Metallurgical Quarterly》1997,179(14):4643-4645
We investigated the capacity of the hyperthermophile Pyrococcus furiosus for DNA repair by measuring survival at high levels of 60Co gamma-irradiation. The P. furiosus 2-Mb chromosome was fragmented into pieces ranging from 500 kb to shorter than 30 kb at a dose of 2,500 Gy and was fully restored upon incubation at 95 degrees C. We suggest that recombination repair could be an extremely active repair mechanism in P. furiosus and that it might be an important determinant of survival of hyperthermophiles at high temperatures. 相似文献
92.
Purified cell-envelope polyphosphatase as well as polyphoshatase activities of cytosol and isolated vacuoles, of nuclei and mitochondria of the yeast Saccharomyces cerevisiae were compared. The polyphosphatases of cell envelope and cytosol are similar, the polyphosphatases of nuclei, vacuoles and mitochondria differ in their kinetic properties, substrate specificity, requirements in divalent cations and in some effector actions both from these and from each other. 相似文献
93.
1. A total of 360 Japanese quail of 4 commercial meat-type lines and two diet treatments (260 and 216 g/kg or 238 and 195 g/kg of crude protein (CP) in the starter and grower diet, respectively) were used. 2. The positive effect of a high CP diet on body weight was significant only for the first 4 weeks after hatching. 3. The mean age at inflection point of the growth curve (t+) across lines and sexes was 1.4 d (0.6 to 2.8 d within line/sex groups) earlier for quail fed on a high CP diet than in quail receiving a low CP diet. The inflection (y+) and asymptotic (A) weights were similar under both dietary protein concentrations. Nevertheless, the shape of the growth curve, characterised by the ratio y+/A and parameter of the maturing rate k, was significantly influenced by diet. 4. A higher food intake and less efficient food conversion were found for quail fed on a high CP diet in the period from 15 to 28 d of age. 5. The fattening traits such as body weight, cumulative food intake and food conversion, were not affected by dietary CP content at the age of 5 weeks. 6. The effects of line on body weight, food intake and food conversion are discussed. 相似文献
94.
M Fern? PO Bendahl A Brisfors K Byman M Ekeberg L Ferraud K Grankvist B Hjalmers A Nilsson G Sellberg L Skoog O St?l I Wingmo 《Canadian Metallurgical Quarterly》1997,36(8):793-798
Estrogen and progesterone receptor analysis results were compared within and between six laboratories in Sweden using frozen breast cancer cytosol samples, and the same technique (enzyme immunoassay, Abbott Laboratories). The concordance in receptor status (positive vs. negative) was excellent (98.4% (571/580)). The discordant results were attributable to values near cut-off (n = 4) or outliers (n = 5), the latter probably being due to analytical errors. One laboratory reported significantly higher ER concentrations than the others; thus caution should be observed when comparing absolute values from different centers. For PgR there were similar differences between the laboratories. However, the intra- and inter-laboratory differences were small compared with the overall variability in ER and PgR content between different samples in a large database. The range of the median intra-laboratory coefficient of variation was 11-23% for ER and 12-19% for PgR, indicating that there is room for improvement in the quality of assay performance. 相似文献
95.
K Giesen T Hummel A Stollewerk S Harrison A Travers C Kl?mbt 《Canadian Metallurgical Quarterly》1997,124(12):2307-2316
Two classes of glial cells are found in the embryonic Drosophila CNS, midline glial cells and lateral glial cells. Midline glial development is triggered by EGF-receptor signalling, whereas lateral glial development is controlled by the gcm gene. Subsequent glial cell differentiation depends partly on the pointed gene. Here we describe a novel component required for all CNS glia development. The tramtrack gene encodes two zinc-finger proteins, one of which, ttkp69, is expressed in all non-neuronal CNS cells. We show that ttkp69 is downstream of gcm and can repress neuronal differentiation. Double mutant analysis and coexpression experiments indicate that glial cell differentiation may depend on a dual process, requiring the activation of glial differentiation by pointed and the concomitant repression of neuronal development by tramtrack. 相似文献
96.
A monitoring of tool wear in different cutting operations has been studied for many years. Special techniques have been used to detect a wear status basing upon cutting forces, acoustic emission, temperature, torque and power, vibration, noise and acceleration sensors. The adapting of a proper prediction method allows to solve problems of an automatic supervision in Computer Integrated Manufacturing systems. A task of the abrasive edge wear index prediction can be formulated as follows: disposing by the data collection of the edge wear status in a time period preceding the concerning the wear status in the successive time period embraced by the prediction method. 相似文献
97.
Z. Yu Y. F. Hsia X. Z. You H. Spiering P. Gutlich 《Journal of Materials Science》1997,32(24):6579-6581
A light-induced excited spin state trapping (LIESST) experiment for a thermal gradual spin crossover complex, Fetris (2-pyridylmethyl)
amine(NCS)2 or Fe(tpa) (NCS)2, was attempted for the first time. The high spin (HS) state after light inducement stayed metastable
over a period of days without relaxation at 10 K. Intersystem relaxation from a high to a low spin (LS) complex occurred at
50 K after bleaching at 10 K. Investigation of the Mossbauer spectra of the LIESST and relaxation experiment indicated that
the Debye–Waller factor was a correlation parameter of the HS fraction and that the co-operative effect played a role in the
relaxation process for such a solid compound.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
98.
99.