全文获取类型
收费全文 | 6333篇 |
免费 | 106篇 |
国内免费 | 11篇 |
专业分类
电工技术 | 261篇 |
综合类 | 4篇 |
化学工业 | 1088篇 |
金属工艺 | 194篇 |
机械仪表 | 113篇 |
建筑科学 | 85篇 |
矿业工程 | 1篇 |
能源动力 | 185篇 |
轻工业 | 430篇 |
水利工程 | 23篇 |
石油天然气 | 4篇 |
无线电 | 790篇 |
一般工业技术 | 1021篇 |
冶金工业 | 1740篇 |
原子能技术 | 177篇 |
自动化技术 | 334篇 |
出版年
2023年 | 19篇 |
2022年 | 52篇 |
2021年 | 81篇 |
2020年 | 35篇 |
2019年 | 40篇 |
2018年 | 84篇 |
2017年 | 58篇 |
2016年 | 98篇 |
2015年 | 59篇 |
2014年 | 104篇 |
2013年 | 211篇 |
2012年 | 156篇 |
2011年 | 208篇 |
2010年 | 164篇 |
2009年 | 174篇 |
2008年 | 204篇 |
2007年 | 200篇 |
2006年 | 193篇 |
2005年 | 170篇 |
2004年 | 170篇 |
2003年 | 178篇 |
2002年 | 157篇 |
2001年 | 150篇 |
2000年 | 161篇 |
1999年 | 192篇 |
1998年 | 640篇 |
1997年 | 406篇 |
1996年 | 268篇 |
1995年 | 210篇 |
1994年 | 204篇 |
1993年 | 187篇 |
1992年 | 104篇 |
1991年 | 91篇 |
1990年 | 97篇 |
1989年 | 95篇 |
1988年 | 84篇 |
1987年 | 76篇 |
1986年 | 72篇 |
1985年 | 78篇 |
1984年 | 57篇 |
1983年 | 54篇 |
1982年 | 57篇 |
1981年 | 57篇 |
1980年 | 35篇 |
1979年 | 43篇 |
1978年 | 29篇 |
1977年 | 45篇 |
1976年 | 73篇 |
1975年 | 14篇 |
1973年 | 11篇 |
排序方式: 共有6450条查询结果,搜索用时 15 毫秒
921.
S Suzuki Y Maruyama T Nakamura M Ueno S Nishi A Ooshima M Isemura M Arakawa 《Canadian Metallurgical Quarterly》1994,66(4):462-469
A 35-year-old male patient clinically characterized by massive proteinuria and hypertension without evidence of systemic diseases is reported. Histological investigation of renal biopsy specimens revealed extensive nodular formations in the mesangial areas in every glomerulus. Light-microscopic examination did not allow discrimination between the glomerular changes found in these specimens and the nodular glomerulosclerosis described in patients with diabetes mellitus. Electron-microscopic examination confirmed the presence of massive, nodular, mesangial expansions consisting of finely fibrillar substances without electron-dense deposits and circumferential mesangial interposition. Immunofluorescent examination showed deposition of IgG, C3, fibrinogen and kappa and lambda light chains in mesangial areas, peripheral capillary loops and a part of the nodules. Furthermore, collagen types IV, V, VI and laminin were detected in the nodules. Amyloid was not observed in these nodules. This diagnosis has not been made, and the mechanism of this nodular glomerulosclerosis remains unknown. 相似文献
922.
The low-resolution (2 nm) subunit symmetry of cucurbitin, the crystalline seed storage globulin of cucurbits, has been determined by X-ray diffraction. The wet crystals belong to the cubic space group F23 and there are 4 molecules per unit cell. The molecules therefore possess point-group symmetry 23 and contain 12 structural units which at this resolution are indistinguishable. On drying, the crystal lattice dimension shrinks from 13.6 nm to 12.4 nm with no apparent change in symmetry. Diffraction patterns of small crystals spun into a pellet, and sections of dry and wet native seed indicate that in situ the protein is organised in microcrystals of the same unit cell and symmetry. Edestin, the crystalline storage globulin from cannabis, and a crystalline globulin from tobacco seed both have the same crystal lattice as cucurbitin and, very likely, the same subunit symmetry. 相似文献
923.
F Imai T Suzuki T Ishibashi M Tanaka Y Akiyama Y Dohi 《Canadian Metallurgical Quarterly》1994,21(4):612-615
OBJECTIVE: We investigated the in vitro immunomodulatory effects of sulfasalazine on B cells in rheumatoid arthritis (RA). METHODS: Reversed hemolytic plaque assay and 3H-thymidine incorporation were measured. RESULTS: B cells from patients with RA showed hyperactivity to stimulation by Staphylococcus aureus Cowan I. Sulfasalazine significantly inhibited this B cell hyperactivity in a dose dependent manner. The kinetic study and a decrease in 3H-thymidine incorporation on Day 3 indicate that sulfasalazine inhibited the early phase (0-48 h) of B cell proliferation in these patients. Sulfapyridine also inhibited B cell hyperactivity in these patients, but 5-aminosalicylic acid and N-acetylsulfapyridin had no significant effect. CONCLUSION: Sulfasalazine exhibited a direct immunosuppressive effect on B cell hyperactivity in patients with RA, which may be responsible for its therapeutic effectiveness in this disorder. 相似文献
924.
Surface characteristics of the bovine oocyte and its investments before, during, and after maturation, and fertilization in vitro were evaluated by scanning electron microscopy (SEM). Oocyte diameters were also measured during SEM analysis of the oocyte. The cumulus cells manifested a compact structure with minimal intercellular spaces among them in the immature oocytes. These became fully expanded with increased intercellular spaces after maturation in vitro, but contracted again after fertilization. The zona pellucida (ZP) showed a fibrous, open mesh-like structure in the maturing and matured oocytes. The size and number of meshes on the ZP decreased dramatically after fertilization. The vitelline surface of immature oocytes was characterized by distribution of tongue-shaped protrusions (TSPs) varying in density. After 10 and 22 hr of maturation incubation, oocyte surface microvilli (MV) increased to become the predominant surface structure, and TSPs decreased substantially. The vitelline surface of fertilized oocytes (at 6 and 20 hr) was similar to that of the matured oocytes, but unfertilized oocytes had less dense MV than did fertilized oocytes (at 20 hr). The diameter of the oocytes decreased from 99 to 80 microns during maturation and increased to 106 microns after insemination (P < 0.05). Membrane maturation was characterized by surface changes from a TSP-predominant pattern to a MV-predominant pattern. Thus, the bovine oocyte maturation process was found to involve the expansion of cumulus cells and the maturation of the ZP, which changes dramatically upon fertilization. Also, volumetric changes occurred in ooplasm processed for SEM following oocyte maturation and insemination. 相似文献
925.
Vertical seismic response of overhead crane 总被引:1,自引:0,他引:1
Vertical seismic response behavior is an important issue for the seismic design of equipments. The equipment, which is comparatively soft and unrestrained vertically, may resonate and its response is significantly magnified under vertical seismic excitation. Overhead crane is an example of equipment that is unrestrained vertically. The dynamic behavior of an 150-ton-capacity overhead crane under vertical seismic excitation was investigated by scale model excitation test and nonlinear time history analysis. The excitation tests were performed with several input levels and the vertical response with each input level was obtained. The simulation analysis approximately corresponded to the results of the excitation test. 相似文献
926.
N Kagimoto Y Masubuchi S Fujita S Narimatsu T Suzuki 《Canadian Metallurgical Quarterly》1994,46(6):528-530
The effect of repetitive oral administration of propranolol (100 mg kg-1 day-1, 5 days) on the kinetics of liver microsomal propranolol metabolism was investigated in the rat. Vmax values of the high-affinity phase for biphasic kinetics of propranolol 4- and 5-hydroxylase activities were decreased by propranolol pretreatment, while those of the low-affinity phase were unchanged. The Vmax value of monophasic 7-hydroxylase activity was also decreased. On the other hand, the Vmax value of N-desisopropylase activity in the propranolol-treated rats was increased more than 2-fold compared with non-treated (control) rats, resulting in a change from monophasic in control rats to biphasic kinetics in propranolol-treated rats. These findings indicate that repetitive administration of propranolol selectively impairs a CYP2D isozyme that is involved in the high-affinity phases for propranolol ring-hydroxylations. 相似文献
927.
To evaluate left ventricular diastolic filling properties in elderly hypertensive case with left ventricular hypertrophy (LVH), we investigated the influence of postural change from a supine to sitting position on transmitral flow velocity profile as assessed by pulsed Doppler echocardiography in 12 normotensives (N group) and 24 hypertensives, aged 65 to 80 years. Hypertensive subjects were divided into two groups on the basis of left ventricular mass index (LVMI): 12 hypertensives without LVH (H1 group; LVMI < 130 g/m2); 12 hypertensives with LVH (H2 group; LVMI > 130 g/m2). Peak early filling velocity (E), peak atrial filling velocity (A) and the E/A ratio were similar in the three groups in the supine position. The postural change decreased E and A in N and H1 groups. On the other hand, the change decreased E, but not A in the H2 group. The E/A ratio was decreased in the H2 group compared with both the N and H1 group in the sitting position. As a result, the sitting position increased atrial contribution to diastolic filling in the H2 group. These observations indicate that a reduction in preload changes the transmitral flow velocity profile in elderly hypertensives with left ventricular hypertrophy. The Doppler alterations may be related to impaired left ventricular diastolic function. 相似文献
928.
The prevalence of normal tension glaucoma (NTG) or primary open angle glaucoma (POAG) is higher in myopic populations and the prevalence of myopia and NTG is relatively high in the Japanese. To evaluate the influence of myopic refractive error on the central visual field defect in NTG eyes, the data obtained from NTG eyes with the Humphrey Visual Field Analyser were analysed in comparison with those from POAG eyes. One hundred and twenty NTG eyes and one hundred and ninety-seven POAG eyes were included. All of them had clear ocular media, but no myopic degeneration in the fundus. Multiple linear regression analysis was performed with a dependent variable of the deviation of the measured threshold value from normal reference value (total deviation, STATPAC) and independent variables of refractive error and mean deviation (STATPAC). Myopic power was found to be positively correlated with the depression in the lower papillo-macular area in both NTG and POAG eyes, and it was negatively correlated with the depression in an upper arcuate area extending just nasal to the fixation only in NTG eyes. 相似文献
929.
A network-theoretic approach to the design of a dynamic precompensator C (s ) for a multiinput, multioutput plant T (s ) is considered. The design is based on the relative degree of each element of T (s ). Specifically, an efficient algorithm is presented for determining whether a given plant T (s ) has a diagonal precompensator C ( s ) such that, for almost all cases, T (s )C (s ) has a diagonal interactor. The algorithm also finds any optimal precompensator, in the sense that the total relative degree is minimal. The algorithm can be easily modified to work even when a T (s ) represented by a nonsquare matrix is given 相似文献
930.
When JFET is used as an amplifier, it should be regarded that the effect of excess gate current on the input impedance is changed by gain of the amplifier. The input impedance or conductance with gain of the JFET amplifier is experimentally analyzed applying small signal equivalent circuit. 相似文献