全文获取类型
收费全文 | 1212篇 |
免费 | 12篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 4篇 |
化学工业 | 31篇 |
金属工艺 | 7篇 |
机械仪表 | 11篇 |
建筑科学 | 43篇 |
矿业工程 | 1篇 |
能源动力 | 4篇 |
轻工业 | 42篇 |
水利工程 | 5篇 |
石油天然气 | 23篇 |
无线电 | 19篇 |
一般工业技术 | 29篇 |
冶金工业 | 835篇 |
原子能技术 | 1篇 |
自动化技术 | 170篇 |
出版年
2023年 | 8篇 |
2020年 | 8篇 |
2019年 | 7篇 |
2018年 | 9篇 |
2017年 | 10篇 |
2016年 | 6篇 |
2014年 | 7篇 |
2013年 | 29篇 |
2012年 | 8篇 |
2011年 | 13篇 |
2009年 | 15篇 |
2008年 | 12篇 |
2007年 | 7篇 |
2006年 | 15篇 |
2005年 | 14篇 |
2004年 | 12篇 |
2003年 | 16篇 |
2002年 | 10篇 |
2001年 | 9篇 |
2000年 | 13篇 |
1999年 | 22篇 |
1998年 | 235篇 |
1997年 | 140篇 |
1996年 | 83篇 |
1995年 | 57篇 |
1994年 | 59篇 |
1993年 | 53篇 |
1992年 | 10篇 |
1991年 | 20篇 |
1990年 | 17篇 |
1989年 | 24篇 |
1988年 | 17篇 |
1987年 | 17篇 |
1986年 | 17篇 |
1985年 | 18篇 |
1984年 | 5篇 |
1983年 | 10篇 |
1982年 | 5篇 |
1981年 | 10篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1978年 | 9篇 |
1977年 | 21篇 |
1976年 | 56篇 |
1975年 | 15篇 |
1974年 | 7篇 |
1973年 | 10篇 |
1972年 | 5篇 |
1968年 | 5篇 |
1965年 | 6篇 |
排序方式: 共有1225条查询结果,搜索用时 0 毫秒
51.
A simple method for the analysis of polyacrylamide diffusive gradients in thin film (DGT) gels by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS), employing a novel use of (115)In internal standardization, has been developed. This method allows the determination of Co, Ni, Cu, Zn, Cd, and Pb concentrations (at the DGT filter face) or fluxes in sediments at a spatial resolution of 100 microm. Single-layered gels, using an optimized laser defocus of 4000 microm at 400 mJ power, showed high precision (generally approximately 10%) and a linear response during solution deployment. Of the elements Sc, In, Ba, La, Ce, and Tb, Ba most closely tracked variations in laser energy and showed the highest analytical precision but could not be used as an internal standard due to its elevated presence in natural sediments. Therefore, internal standardization, necessary to normalize data collected on different days, was carried out using (115)In contained within a second layer of backing gel and dried along with the analyte layer as a dual-gel disk. This multilayered gel standard required a laser defocus setting of 1000 microm and a laser power of approximately 800 mJ. Analytical precision for a 64-spot ablation grid at 100-microm spacing was approximately 10%. Verification of this method was carried out on DGT sediment probes deployed in Priest Pot (English Lake District). Results obtained by conventional slicing techniques and aqueous elution agreed with laser ablation results when the different sampling areas were considered. The elution results varied by a factor of <2, whereas the laser ablation technique showed a variability of approximately 4, indicating localized elevated concentrations of Co. This higher resolution LA-ICPMS method could ultimately lead to an improved understanding of the geochemical processes responsible for metal uptake and release in sediments. 相似文献
52.
53.
54.
NE Taylor RN Rosenthal B Chabus S Levine AS Hoffman J Reynolds L Santos I Willets P Friedman 《Canadian Metallurgical Quarterly》1993,15(1):36-40
Cryptococcal meningitis has a high mortality rate of central nervous infection. The patients usually die of the disease itself, or complications from increased intracranial pressure. Early diagnosis and treatment, including surgical drainage, will improve the results. In this series, twenty-one patients with high intracranial pressure (ICP > 300 mmH2 O) are presented. Fourteen received implantation of Ommaya reservoir to aspirate cerebrospinal fluid (CSF) for relief of symptoms of ICP. Meanwhile 4 of these 14 patients also received intraventricular injection of amphotericin B because of poor response to systemic drugs. Another seven patient received systemic drug therapy only. Survival during therapy occurred in 11 of 14 patients in the surgical group, compared with only 1 of 7 patients treated by drug therapy alone (P = 0.019). In the 14 patients who received implantation of an Ommaya reservoir, there was one complication of CSF leakage when the reservoir ruptured because of repeated aspiration. For patients with cryptococcal meningitis with high ICP, early implantation of an Ommaya reservoir will improve the survival rate. 相似文献
55.
Although self-help/mutual-help groups, like Alcoholics Anonymous, are important factors in the recovery of many chemically dependent individuals, the large dropout rates from such groups and the awareness that many who drop out do not return to dependent behavior raises interesting questions about other paths to sustained abstinence and recovery. Current emphasis on treatment outcome studies provides a means for researching factors in both those who recover with and without the assistance of self-help/mutual-help groups. The authors suggest some questions which might be investigated. 相似文献
56.
LM Powell DT Dryden DF Willcock RH Pain NE Murray 《Canadian Metallurgical Quarterly》1993,234(1):60-71
The methyltransferase of the EcoK type I restriction/modification system is trimeric, M2S1, where the S subunit determines the sequence specificity of the enzyme. The methyltransferase has a strong preference for hemimethylated substrate DNA and, therefore, we have investigated the effect of the methylation state of DNA on binding by the enzyme, together with the effects on binding of the cofactor S-adenosyl-L-methionine. Our results indicate that the methyltransferase has two non-interacting S-adenosyl-L-methionine binding sites, each with a dissociation constant of 3.60 (+/- 0.42) microM determined by equilibrium dialysis, or 2.21 (+/- 0.29) microM determined by the displacement of a fluorescent probe. Ultraviolet light-induced crosslinking showed that S-adenosyl-L-methionine binds strongly only to the modification (M) subunits. Changes in the sedimentation velocity of the methyltransferase imply a protein conformational change due to S-adenosyl-L-methionine binding. Gel retardation results show that the binding of S-adenosyl-L-methionine to the methyltransferase enhances binding to both specific and non-specific DNAs, but the enhancement is greater for the specific DNA. Differences in binding affinities contribute to the recognition of the specific nucleotide sequence AAC(N)6GTGC by the methyltransferase in preference to a non-specific sequence. In contrast, although the complexes of unmodified and hemimethylated DNAs with the methyltransferase have different mobilities in non-denaturing gels, there appears to be no contribution of binding affinity to the distinction between these two substrates. Therefore, the preference for a hemimethylated substrate must be due to a difference in catalysis. 相似文献
57.
AR Vaccaro SC Ludwig GR Klein M McQuire D Green NE Green 《Canadian Metallurgical Quarterly》1998,27(11):746-748
We report on two patients who developed bilateral peroneal nerve palsy after using a knee board behind a water ski boat. This device causes the rider's knees to be in a hyperflexed position secured with a strap across the thighs. Treatment for this compressive neuropathy is conservative. Recreational users may wish to limit the duration and frequency of participation in this sport, thus decreasing the predisposition to prolonged nerve compression. In addition, manufacturers may consider making fundamental design changes such as padding the nylon straps or outrigger devices that contact the proximal lateral tibia. 相似文献
58.
This paper considers the robust stability of a linear time-invariant state space model subject to real parameter perturbations.
The problem is to find the distance of a given stable matrix from the set of unstable matrices. A new method, based on the
properties of the Kronecker sum and two other composite matrices, is developed to study this problem; this new method makes
it possible to distinguish real perturbations from complex ones. Although a procedure to find the exact value of the distance
is still not available, some explicit lower bounds on the distance are obtained. The bounds are applicable only for the case
of real plant perturbations, and are easy to compute numerically; if the matrix is large in size, an iterative procedure is
given to compute the bounds. Various examples including a 46th-order spacecraft system are given to illustrate the results
obtained. The examples show that the new bounds obtained can have an arbitrary degree of improvement over previously reported
ones.
This work has been supported by the Natural Sciences and Engineering Research Council of Canada under Grant No. A4396. 相似文献
59.
The effect of the dielectric constant on unipolar and bipolar charging rates is investigated. This effect is manifested through the image potential. Bulk dielectric constants of aerosol materials range from 2.5 to 50. The corresponding image potentials range from about 40% to about 96% of the image potential for a perfect conductor. Charging simulations were carried out for this parameter range and typical results are presented. For dielectric constants greater than 2.5 the charging behavior shows a strong image potential effect, and may be approximated by calculations for a perfect conductor. This suggests that charging models that do not allow for image potential effects are likely to be inaccurate except, perhaps, for larger particles, where the Coulomb potential dominates the image potential. The simulations are compared with unipolar charging data from recent experiments, which tend also to support this conclusion. 相似文献
60.
M Wartmann N Cella P Hofer B Groner X Liu L Hennighausen NE Hynes 《Canadian Metallurgical Quarterly》1996,271(50):31863-31868