全文获取类型
收费全文 | 1773篇 |
免费 | 21篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 20篇 |
化学工业 | 122篇 |
金属工艺 | 22篇 |
机械仪表 | 21篇 |
建筑科学 | 26篇 |
矿业工程 | 4篇 |
能源动力 | 18篇 |
轻工业 | 78篇 |
水利工程 | 5篇 |
石油天然气 | 5篇 |
无线电 | 145篇 |
一般工业技术 | 204篇 |
冶金工业 | 1027篇 |
原子能技术 | 15篇 |
自动化技术 | 84篇 |
出版年
2021年 | 11篇 |
2019年 | 6篇 |
2018年 | 15篇 |
2017年 | 12篇 |
2016年 | 9篇 |
2015年 | 9篇 |
2014年 | 11篇 |
2013年 | 42篇 |
2012年 | 24篇 |
2011年 | 40篇 |
2010年 | 24篇 |
2009年 | 21篇 |
2008年 | 30篇 |
2007年 | 47篇 |
2006年 | 29篇 |
2005年 | 23篇 |
2004年 | 24篇 |
2003年 | 26篇 |
2002年 | 24篇 |
2001年 | 27篇 |
2000年 | 11篇 |
1999年 | 50篇 |
1998年 | 282篇 |
1997年 | 174篇 |
1996年 | 128篇 |
1995年 | 78篇 |
1994年 | 51篇 |
1993年 | 65篇 |
1992年 | 18篇 |
1991年 | 40篇 |
1990年 | 42篇 |
1989年 | 38篇 |
1988年 | 33篇 |
1987年 | 23篇 |
1986年 | 27篇 |
1985年 | 37篇 |
1984年 | 7篇 |
1983年 | 20篇 |
1982年 | 15篇 |
1981年 | 16篇 |
1980年 | 22篇 |
1979年 | 16篇 |
1978年 | 12篇 |
1977年 | 26篇 |
1976年 | 44篇 |
1975年 | 8篇 |
1974年 | 9篇 |
1973年 | 6篇 |
1970年 | 6篇 |
1969年 | 5篇 |
排序方式: 共有1796条查询结果,搜索用时 15 毫秒
1.
Water Resources Management - Public awareness of water quality concerns has increased since the Flint, MI crisis, but knowledge about water resources management remains low. Consequently,... 相似文献
2.
Adaptive increases in renal bicarbonate reabsorption occur in response to acute increases in filtered bicarbonate (FLHCO3). In a previous study, we showed that an increase in FLHCO3 induced by plasma volume expansion increased the Vmax for Na+/H+ exchange activity in renal cortical brush border membrane vesicles (BBMV), providing a potential mechanism for the adaptive increase in HCO3- reabsorption. The present studies were undertaken to determine whether the increase in FLHCO3 induced by plasma expansion also stimulates the other major H+ transporter in cortical BBMV, the H(+)-ATPase. H(+)-ATPase activity was assessed in BBMV obtained from hydropenic and plasma expanded Munich-Wistar rats, using a NADH-linked ATPase assay. H(+)-ATPase activity was measured as the ouabain and oligomycin-insensitive, bafilomycin A1-sensitive component of total ATPase activity. Acute plasma expansion doubled single nephron FLHCO3, and this change was associated with a 64% increase in the Vmax for H(+)-ATPase activity, with no change in apparent Km. The Vmax for H(+)-ATPase activity correlated directly with whole kidney GFR and FLHCO3 (r = 0.68 and 0.72, respectively), and with single nephron GFR and FLHCO3 (r = 0.76 and 0.80, respectively). Thus, the mechanism for the adaptive increase in proximal tubular HCO3- reabsorption that occurs in response to acute increases in FLHCO3 appears to be related to increased activity of both H(+)-ATPase and Na+/H+ exchange in the apical membrane of the proximal tubule epithelium. 相似文献
3.
4.
Recordings from the central branches of single identified dactyl sensory afferent (DSA) neurons in a crayfish in vitro preparation were performed to study modifications of the sensory message occurring before the first central synapse. These afferents comprised hairs and force-sensitive mechanoreceptors with phasic and phasotonic response characteristics in the terminal segment (dactyl) of the crayfish leg. More than one afferent spike size was often observed in intracellular recordings from these afferents, thus indicating the presence of electrical coupling between the central processes of DSA fibers. Additionally, in identified DSA fibers with large spike sizes, primary afferent depolarizations (PADs) of up to 15 mV were observed, which sometimes triggered antidromic spikes in the afferent. Nevertheless, PADs were clearly inhibitory, because they shunted the afferent spikes. They exhibited the following properties. First, each PAD was preceded by an afferent spike from a neighboring hair, indicating that the PADs had a sensory rather than central origin. Second, PADs could follow high frequencies of afferent discharges without failure, a property suggestive of monosynaptic connections, but because PAD latencies varied by +/-0.5 ms it is more likely that they were mediated by a disynaptic pathway. Third, although PADs were evoked in an extremely reliable manner, their amplitude varied in a quantal manner. Most unitary PADs were the result of the release of < 12 quanta, the mean quantal content lying between 4 and 5; quantal size was large, approximately 1 mV. Fourth, PADs showed facilitation in some fibers, whereas in others they became much smaller when occurring at brief intervals. We suggest that PADs may be an efficient and parsimonious way to limit sensory inflow in space and time, allowing the crayfish to identify precisely both weak and strong mechanical stimuli. 相似文献
5.
Even without electrolyte imbalance, dehydration and fever, seizures are found occasionally in the cases of mild diarrhea. Such patients have shown favorable outcome during long-term follow-up. Twenty cases (10 boys and 10 girls) of benign seizure with mild diarrhea have been diagnosed at the Pediatric Department of Cathay General Hospital from January 1987 to March 1991. Ages-of-onset ranged from 3 months to 43 months (mean 19 months). Most cases were found between December and March (16 cases, 80%). Most seizure episodes were from 2 to 5 times (10 cases, 50%); the durations of seizures were mostly within a 5-minute period (16 cases, 80%). All seizures were generalized and symmetric, including tonic-clonic (13 cases, 65%), tonic (5 cases, 25%), and clonic (2 cases, 10%). Six out of 11 cases (54.5%) showed Rotazyme (Latex agglutination) positive. After six month to four year follow up, no patient had suffered any type of epilepsy, and psychomotor development was normal in all. Further discussion of clinical features is provided. 相似文献
6.
7.
8.
YC Lo L Brett CJ Kenyon SD Morley JI Mason BC Williams 《Canadian Metallurgical Quarterly》1998,24(3-4):559-563
We have employed polyclonal antibodies to a peptide sequence of bovine steroidogenic acute regulatory (StAR) protein and human placental 3beta-hydroxysteroid dehydrogenase (3beta-HSD) to determine the localisation and distribution of these proteins in rat and bovine adrenal glands. Immunohistochemical staining demonstrated the presence of StAR protein in the zona glomerulosa (ZG), zona fasciculata (ZF), zona reticularis (ZR) and in the medulla of both species. For 3beta-HSD, immunostaining was observed in the ZG, ZF and ZR of the rat adrenal and was absent in the medulla. Immunoblotting experiments showed intense bands for StAR protein (30 kDa, 37 kDa) in the mitochondria of bovine ZG, ZF and medulla and a less intense band (30 kDa) in the microsomes. In rat ZG and ZF/R mitochondria only the 30 kDa protein was present. For 3beta-HSD, an intense band (42 kDa) was found in microsomes and mitochondria of rat and bovine ZG and ZFR. A very faint signal for 3beta-HSD was seen in adrenal medulla. In conclusion, StAR (or a closely related) protein is present throughout the adrenal gland in rat and bovine species in contrast to 3beta-HSD which is confined to the steroidogenic zones. The possible function of StAR protein in the adrenal medulla merits investigation. 相似文献
9.
The effect of particle distribution on damage formation in particulate reinforced metal matrix composites deformed in compression 总被引:1,自引:0,他引:1
P.B. Prangnell S.J. Barnes S.M. Roberts P.J. Withers 《Materials Science and Engineering: A》1996,220(1-2):41-56
Image analysis results are reported on the generation of damage in particulate reinforced metal matrix composites during compressive deformation. The technique allows the automated collection of data on the incidence of particle fracture and void formation in the matrix as a function of important microstructural parameters such as local particle volume fraction and particle size. There is a strong relationship between damage and the local volume fraction of the reinforcement proving that damage formation is accentuated in regions of particle clustering. With the SiC reinforced materials examined, there was observed to be a change in dominance of damage mechanism from particle fracture at low local volume fractions to void formation in the matrix within strongly clustered regions. The results are compared with finite element (FE) modelling of the compressive deformation of clustered particles using a simple cluster of equi-spaced particles. The FE results suggest that plastic flow is generally inhibited in clustered regions. In certain highly clustered configurations shielding is such that flow does not occur in the heart of the cluster even at high levels of average plastic strain. The modelling suggests that the change in dominance of damage mechanism is related to the dramatic increase in tensile hydrostatic stresses in the matrix with higher levels of particle clustering. 相似文献
10.
D Levine PD Barnes S Sher RC Semelka W Li CR McArdle S Worawattanakul RR Edelman 《Canadian Metallurgical Quarterly》1998,206(2):549-554
PURPOSE: To evaluate the normal appearance of fetal anatomy, the conspicuity of fetal organs, the reproducibility of images, and the limitations to image quality with the use of half-Fourier, single-shot rapid acquisition with relaxation enhancement (RARE) magnetic resonance (MR) imaging. MATERIALS AND METHODS: Fifty-four fetuses of 49 pregnancies underwent MR imaging with the half-Fourier, single-shot RARE technique. Two reviewers attempted to identify 47 organs and anatomic regions in each fetus. Organ or region conspicuity, image quality, and the limitations of image quality were graded. RESULTS: Fetal anatomy was well depicted in fetuses over 20 weeks in gestational age. Fetal imaging was limited by gestational age of 20 weeks or less usually owing to the small size of the organ or region being evaluated and, less frequently, by motion. CONCLUSION: Half-Fourier, single-shot RARE MR imaging provided a detailed and reproducible evaluation of normal fetal anatomy, which can be used as a standard of reference in MR imaging of fetal anomalies. 相似文献