全文获取类型
收费全文 | 3671篇 |
免费 | 57篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 61篇 |
综合类 | 5篇 |
化学工业 | 423篇 |
金属工艺 | 53篇 |
机械仪表 | 36篇 |
建筑科学 | 93篇 |
矿业工程 | 18篇 |
能源动力 | 40篇 |
轻工业 | 287篇 |
水利工程 | 12篇 |
石油天然气 | 3篇 |
无线电 | 78篇 |
一般工业技术 | 266篇 |
冶金工业 | 2114篇 |
原子能技术 | 13篇 |
自动化技术 | 228篇 |
出版年
2022年 | 26篇 |
2021年 | 34篇 |
2020年 | 17篇 |
2019年 | 19篇 |
2018年 | 36篇 |
2017年 | 21篇 |
2016年 | 46篇 |
2015年 | 45篇 |
2014年 | 42篇 |
2013年 | 68篇 |
2012年 | 51篇 |
2011年 | 82篇 |
2010年 | 67篇 |
2009年 | 57篇 |
2008年 | 65篇 |
2007年 | 81篇 |
2006年 | 39篇 |
2005年 | 47篇 |
2004年 | 40篇 |
2003年 | 46篇 |
2002年 | 35篇 |
2001年 | 29篇 |
2000年 | 25篇 |
1999年 | 87篇 |
1998年 | 690篇 |
1997年 | 355篇 |
1996年 | 248篇 |
1995年 | 131篇 |
1994年 | 138篇 |
1993年 | 140篇 |
1992年 | 40篇 |
1991年 | 45篇 |
1990年 | 51篇 |
1989年 | 48篇 |
1988年 | 39篇 |
1987年 | 32篇 |
1986年 | 33篇 |
1985年 | 40篇 |
1984年 | 20篇 |
1983年 | 21篇 |
1982年 | 29篇 |
1981年 | 22篇 |
1980年 | 36篇 |
1979年 | 17篇 |
1978年 | 16篇 |
1977年 | 62篇 |
1976年 | 101篇 |
1975年 | 25篇 |
1974年 | 15篇 |
1973年 | 15篇 |
排序方式: 共有3730条查询结果,搜索用时 15 毫秒
31.
The permeability and lag time for a heterogeneous diffusion system, in which the diffusivity and partition coefficient for the diffusant are dependent on position, are formulated in terms of a linear asymptotic analysis. A repeated integration of the diffusion equation is used to obtain the time dependence of the total solute release into the receiver, Q(t). The asymptotic form of Q(t) is linear in time. The slope, and intercept of this linear asymptote with the time axis, respectively, give formulas for the steady-state permeability and lag time. These formulas are then applied to diffusion systems of multiple laminates, consisting of a series of different homogeneous slabs. Thus, for the first time, a concise treatment of diffusion in multiple laminates is obtained. The formulas are also applied to periodic laminates, consisting of a series of identical slabs, but with position-dependent diffusivity and partition coefficient. We found that the lag time can be well approximated by (nh))2/(6Deff), where n and h are, respectively, the number and thickness of individual lamella, and Deff is an effective diffusivity, for which a relation in terms of the local property distributions is obtained. This approximation becomes more accurate with increasing number of lamellae. At n = 5, the relative error is already within 4%. Finally a procedure is discussed for readily obtaining the lag time for periodic structures consisting of a serial repetition of a multi-laminate. 相似文献
32.
33.
Franz Schauer 《Solar Energy Materials & Solar Cells》2005,87(1-4):235
Basic suppositions and microphysical origin of the occurrence of the space-charge-limited currents (SCLC) are presented in general and for the temperature-modulated space-charge-limited currents (TM-SCLC) in particular. The criteria are given for the spectroscopical method TM-SCLC to be used for localized electron states elucidation in organic semiconducting materials for organic solar cells optimization and modelling. The “visibility “of the localized states by SCLC method, i.e. the power of the SCLC method to distinguish the localized states, is tested by the modelling, varying the temperature, energy position of localized states and their concentration. Generally, it was determined that the SCLC measurements results are more reliable with the increased energy of the states, with their increased concentration and with decreased temperature. The correlation (or its absence) between the measured current and activation energy on applied voltage, expressed by the dependence of preexponential factor of conductivity on activation energy (Meyer–Neldel rule), gives the possibility to determine the energy range where the reconstruction of density of localized states function is reliable. 相似文献
34.
35.
36.
Peter Mertens Christian Stary Konrad Walser Thomas Deelmann Franz Lehner Sebastian Günther Christian Scheer 《WIRTSCHAFTSINFORMATIK》2006,48(4):288-295
Ohne Zusammenfassung 相似文献
37.
38.
RL Hughson JK Shoemaker ME Tschakovsky JM Kowalchuk 《Canadian Metallurgical Quarterly》1996,81(4):1619-1626
The hypothesis that the rate of increase in muscle O2 uptake (VO2mus) at the onset of exercise is influenced by muscle blood flow was tested during forearm exercise with the arm either above or below heart level to modify perfusion pressure. Ten young men exercised at a power of approximately 2.2 W, and five of these subjects also worked at 1.4 W. Blood flow to the forearm was calculated from the product of blood velocity and cross-sectional area obtained with Doppler techniques. Venous blood was sampled from a deep forearm vein to determine O2 extraction. The rate of increase in VO2mus and blood flow was assessed from the mean response time (MRT), which is the time to achieve approximately 63% increase from baseline to steady state. In the arm below heart position during the 2.2-W exercise, blood flow and VO2mus both increased, with a MRT of approximately 30 s. With the arm above the heart at this power, the MRTs for blood flow [79.8 +/- 15.7 (SE)s] and VO2mus (50.2 +/- 4.0 s) were both significantly slower. Consistent with these findings were the greater increases in venous plasma lactate concentration over resting valued in the above heart position (2.8 +/- 0.4 mmol/l) than in the below heart position (0.9 +/- mmol/l). At the lower power, both blood flow and VO2mus also increased more rapidly with the arm below compared with above the heart. These data support the hypothesis that changes in blood flow at the onset of exercise have a direct effect on oxidative metabolism through alterations in O2 transport. 相似文献
39.
The present study was designed to investigate the type and extent of degeneration occurring in the human central auditory system subsequent to profound hearing loss. The authors have examined the size of one population of neurons in the ventral cochlear nucleus in seven subjects with profound hearing loss (audiometric responses poorer than 90-100 dB HL). Six normal subjects, ages 35-78, were used as controls. Cell size in the hearing-impaired subjects ranged from normal to reduced by more than 50 percent. Two factors appear to contribute to the variability in cell size reduction. The correlation coefficient (Spearman rs) of cell size with duration of profound deafness was -0.48, indicating a moderate tendency for neurons to become smaller with longer periods of deafness. The correlation coefficient of cell size with number of surviving cochlear ganglion cells was 0.73, indicating a stronger tendency for neurons to be larger with greater eighth nerve innervation of the cochlear nucleus. Two cases of Scheibe degeneration showed the most severe degenerative change in the central auditory system. 相似文献
40.
GR Bayyari WE Huff RA Norton JK Skeeles JN Beasley NC Rath JM Balog 《Canadian Metallurgical Quarterly》1994,38(4):744-754
Two flocks of Nicholas tom turkeys from separate farms with histories of above-average condemnations for turkey green-liver osteomyelitis complex (TOC) were studied throughout a 16-week growout. Fifty birds from each farm were necropsied each week for 15 weeks, and birds that had green livers, osteomyelitis in the proximal tibia, or swollen joints were cultured for aerobic bacteria along with an equal number of control birds. At processing, TOC lesions and green livers were obtained for bacterial culture and histopathology. Green-liver-associated TOC was not observed until the turkeys were 9 or 10 weeks of age. The incidence of TOC was higher on one farm, which also had a higher incidence of airsacculitis, higher early and weekly mortality, seroconversion to Newcastle disease virus and Mycoplasma meleagridis, and significantly higher average body weights, relative spleen weights, and relative liver weights. Both farms had a high incidence of intestinal lesions and infestation with Ascaridia dissimilis. Histological evaluation of green livers revealed hyperplasia of bile ducts, dilation of sinusoids, and pigment-containing Kupffer's cells, some of which stained positive for iron. The bacterial isolates most frequently cultured from bones and livers were pleomorphic gram-variable coccobacilli, which grew visible colonies only after a series of subcultures and extended incubation. 相似文献