全文获取类型
收费全文 | 476篇 |
免费 | 4篇 |
国内免费 | 2篇 |
专业分类
化学工业 | 11篇 |
金属工艺 | 2篇 |
石油天然气 | 5篇 |
无线电 | 2篇 |
冶金工业 | 460篇 |
自动化技术 | 2篇 |
出版年
2019年 | 1篇 |
2018年 | 3篇 |
2014年 | 1篇 |
2013年 | 1篇 |
2010年 | 1篇 |
2008年 | 1篇 |
2003年 | 4篇 |
2000年 | 1篇 |
1999年 | 15篇 |
1998年 | 148篇 |
1997年 | 78篇 |
1996年 | 63篇 |
1995年 | 46篇 |
1994年 | 28篇 |
1993年 | 32篇 |
1992年 | 2篇 |
1991年 | 9篇 |
1990年 | 4篇 |
1989年 | 7篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1978年 | 1篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1975年 | 1篇 |
1965年 | 1篇 |
1964年 | 1篇 |
排序方式: 共有482条查询结果,搜索用时 31 毫秒
21.
Circulating immune complexes in sera of patients with Burkett's lymphoma and nasopharyngeal carcinoma 总被引:1,自引:0,他引:1
Sera of individuals with Burkitt's lymphoma and nasopharyngeal carcinoma, tested by consumption of hemolytic complement, were found by comparison with healthy individuals to have significantly increased levels of circulating immune complexes. The identity of the immune complexes was established by sucrose density gradient ultracentrifugation, which showed them to sediment between 10 and 19S. As they were adsorbable by rheumatoid factor--Sepharose 4B conjugates, it appeared that these complexes were composed of IgG. The complexes were retained by Concanavalin A--Sepharose columns and eluted by alpha methyl-D-mannoside, suggesting by analogy with model complexes that the antigens might be glycoproteins. 相似文献
22.
23.
24.
Monodisperse FePt nanoparticles with size of 4.5 and 6.0 nm were prepared by simultaneous reduction of platinum acetylacetonate
and thermal decomposition of iron pentacarbonyl in benzylether. The crystallography structure, size, and composition of the
FePt nanoparticles were examined by X-ray diffraction and transmission electron microscopy. Energy dispersive X-ray spectrometry
measurements of individual particles indicate a broad compositional distribution in both the 4.5 and 6 nm FePt nanoparticles.
The effects of compositional distribution on the phase-transition and magnetic properties of the FePt nanoparticles were investigated. 相似文献
25.
26.
27.
A novel method for reducing field inhomogeneity effects in magnetic resonance images is described in this paper. Observing that image degradation arises from B0 inhomogeneity-induced phase accrual during data acquisition, the present method numerically rewinds the accumulated phase in the k-space data based on an initial estimate of the image and a corresponding field map. The rewinding process generates a corrected k-space data set that is subsequently Fourier transformed to produce the final image. In this paper, a theoretical analysis of the method and applications of the technique to magnetic resonance imaging data are presented. The theoretical analysis of the method indicates that it is a general approach applicable to a variety of sequences. Results obtained by applying the method to experimental data acquired with single-shot echo-planar imaging, segmented echo-planar imaging with centric reordering, and spiral sequences demonstrate that it is robust in reducing image degradation induced by B0 inhomogeneity. 相似文献
28.
Irinotecan (CPT-11) is a chemotherapeutic agent that is active in the treatment of a variety of solid tumor malignancies. Diarrhea represents the most common dose-limiting toxicity that is independent of the schedule of administration. A rat model with dose-limiting toxicity profiles that are similar to those observed in patients treated with CPT-11 was developed and used to evaluate the role of interleukin 15 (IL-15) in the modulation of the therapeutic selectivity of CPT-11 in normal rats and rats bearing advanced colorectal cancer. The maximum tolerated dose and lethal dose (LD) of CPT-11 by i.v. push daily x 3 were 150 and 200 mg/kg/day, respectively. CPT-11 at the LD induced a 93-100% incidence of severe diarrhea and an 86-100% incidence of lethality in treated animals. IL-15, a cytokine with multiple mechanisms of action, was used at a 100 or 400 microg/kg/dose with different schedules of administration (3, 8, and 11 doses, i.p.) to protect against CPT-11-induced toxicity. IL-15 offered complete and sustained selective protection against CPT-11-induced delayed diarrhea and lethality. IL-15 also moderately potentiated the antitumor activity of CPT-11 in rats bearing advanced colorectal cancer. Morphological examination of rat intestinal tissues after treatment with LD of CPT-11 revealed dramatic protection of duodenal and colonic tissue architecture by IL-15. CPT-11 alone produced serious damage to duodenal villi and colonic crypts. The results clearly demonstrated the ability of IL-15 to provide significant protection from CPT-11-induced intestinal toxicity with maintenance of antitumor activity, resulting in an increase in the therapeutic index of CPT-11. The clinical relevance of the results obtained in this model system needs to be confirmed. 相似文献
29.
In magnetic resonance imaging, spatial localization is usually achieved using Fourier encoding which is realized by applying a magnetic field gradient along the dimension of interest to create a linear correspondence between the resonance frequency and spatial location following the Larmor equation. In the presence of B0 inhomogeneities along this dimension, the linear mapping does not hold and spatial distortions arise in the acquired images. In this paper, the problem of image reconstruction under an inhomogeneous field is formulated as an inverse problem of a linear Fredholm equation of the first kind. The operators in these problems are estimated using field mapping and the k-space trajectory of the imaging sequence. Since such inverse problems are known to be ill-posed in general, robust solvers, singular value decomposition and conjugate gradient method, are employed to obtain corrected images that are optimal in the Frobenius norm sense. Based on this formulation, the choice of the imaging sequence for well-conditioned matrix operators is discussed, and it is shown that nonlinear k-space trajectories provide better results. The reconstruction technique is applied to sequences where the distortion is more severe along one of the image dimensions and the two-dimensional reconstruction problem becomes equivalent to a set of independent one-dimensional problems. Experimental results demonstrate the performance and stability of the algebraic reconstruction methods. 相似文献
30.
Spontaneous Ni2+ entry (leak), measured as fluorescence quench in fura-2-loaded HL-60 cells at the excitation wavelength of 360 nm, was strongly inhibited by tetrandrine (TET, 100 microM), a Ca2+ antagonist of Chinese herbal origin. Exposure of the cells for 5 min to saponins from Quillaja saponaria (QS, 30 microg/ml), surfactants well known to permeabilize the plasma membrane by complexing with cholesterol, promoted Ni2+ entry without causing fura-2 leak-out. Unexpectedly, TET caused an immediate (within 2.5 min) augmentation of QS-promoted Ni2+ entry; and a 5-min treatment with both TET and QS resulted not only in an enhanced Ni2+ entry, but also a fura-2 leak-out. Ginseng saponins (100 microg/ml) alone or together with TET did not cause such a permeabilization. Permeabilization induced by 1-3 microM digitonin, another cholesterol-complexing glycoside, could not be enhanced by TET. TET did not affect permeabilization induced by Triton X-100 (0.01%), a detergent which non-specifically disrupts the hydrophobic interaction at the plasma membrane. TET also did not enhance Ni2+ entry triggered by ionomycin (0.35 microM) or SK&F 96365 (20 microM). Further, it did not augment Ni2+ entry when the plasma membrane fluidity was modulated by changes of temperature (27-47 degrees C) or treatment with 5% ethanol. This QS-promoted Ni2+ entry could not be amplified by other lipophilic Ca2+ antagonists, such as diltiazem (100 microM) and verapamil (100 microM). The results hence indicate that TET enhanced Ni2+ entry (or permeabilization) elicited by QS treatment, but not other perturbations of the plasma membrane. We suggest that pore formation at the plasma membrane, a consequence of QS-cholesterol interaction, can be specifically enhanced by TET. Also, a comparative study of the effects of TET and its very close analogues, hernandezine and berbamine, reveals that the methoxyl group at the R2 position of TET appears to be crucial in enhancing QS-promoted Ni2+ entry. 相似文献