全文获取类型
收费全文 | 2464篇 |
免费 | 87篇 |
国内免费 | 61篇 |
专业分类
电工技术 | 64篇 |
综合类 | 137篇 |
化学工业 | 149篇 |
金属工艺 | 60篇 |
机械仪表 | 53篇 |
建筑科学 | 48篇 |
矿业工程 | 14篇 |
能源动力 | 36篇 |
轻工业 | 112篇 |
水利工程 | 25篇 |
石油天然气 | 12篇 |
武器工业 | 4篇 |
无线电 | 78篇 |
一般工业技术 | 86篇 |
冶金工业 | 1597篇 |
原子能技术 | 9篇 |
自动化技术 | 128篇 |
出版年
2024年 | 4篇 |
2023年 | 17篇 |
2022年 | 35篇 |
2021年 | 41篇 |
2020年 | 35篇 |
2019年 | 20篇 |
2018年 | 14篇 |
2017年 | 24篇 |
2016年 | 24篇 |
2015年 | 28篇 |
2014年 | 42篇 |
2013年 | 45篇 |
2012年 | 72篇 |
2011年 | 76篇 |
2010年 | 78篇 |
2009年 | 77篇 |
2008年 | 72篇 |
2007年 | 83篇 |
2006年 | 76篇 |
2005年 | 43篇 |
2004年 | 38篇 |
2003年 | 30篇 |
2002年 | 25篇 |
2001年 | 33篇 |
2000年 | 17篇 |
1999年 | 52篇 |
1998年 | 472篇 |
1997年 | 294篇 |
1996年 | 171篇 |
1995年 | 97篇 |
1994年 | 71篇 |
1993年 | 92篇 |
1992年 | 16篇 |
1991年 | 7篇 |
1990年 | 13篇 |
1989年 | 8篇 |
1988年 | 10篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1981年 | 12篇 |
1980年 | 18篇 |
1979年 | 6篇 |
1978年 | 10篇 |
1977年 | 48篇 |
1976年 | 132篇 |
1975年 | 6篇 |
1955年 | 2篇 |
排序方式: 共有2612条查询结果,搜索用时 359 毫秒
41.
42.
A George J Gui NA Jenkins DJ Gilbert NG Copeland A Veis 《Canadian Metallurgical Quarterly》1994,42(12):1527-1531
Dentinogenesis is being used as a model for understanding the biomineralization process. The odontoblasts synthesize a structural matrix comprised of Type I collagen fibrils which define the basic architecture of the tissue. The odontoblasts also synthesize and deliver a number of dentin-specific acidic macromolecules into the extracellular compartment. These acidic macromolecules may be involved in regulating the ordered deposition of hydroxyapatite crystals within the matrix. AG1 is the first tooth-specific acidic macromolecule to have been cloned and sequenced. To identify which cells of the rat incisor pulp/odontoblast complex were responsible for synthesis of AG1, in situ hybridization was used. Digoxigenin labeled sense and anti-sense AG1 riboprobes were prepared. The AG1 mRNA was found to be expressed in the mature secretory odontoblasts. Neither pulp cells nor pre-odontoblasts showed any staining with the anti-sense probes. Chromosomal localization studies placed the AG1 gene on mouse chromosome 5q21, in tight linkage with Fgf5. AG1 has been renamed Dmp1 (dentin matrix protein 1) in accordance with present chromosomal nomenclature. Mouse 5q21 corresponds to the 4q21 locus in humans. This is the locus for the human tooth mineralization disorder dentinogenesis imperfecta Type II (DI-II). These data suggest that the Dmp1 gene is involved in mineralization and is a candidate gene for DI-II. 相似文献
43.
NA Paterson JK Peat CM Mellis W Xuan AJ Woolcock 《Canadian Metallurgical Quarterly》1997,10(3):658-664
Insufficient use of anti-inflammatory drugs, such as inhaled corticosteroids and cromoglycate, may contribute to the disease burden associated with asthma. Conversely, aggressive treatment of mild disease may result in avoidable costs and/or adverse drug effects. The aim of this study was to determine the relationship between asthma severity and inhaled corticosteroid/cromoglycate use in a large (n=4,909) random sample of children, aged 8-11 yrs, in NSW, Australia. Asthma and its treatment were assessed by questionnaire responses. Asthma, defined as diagnosis plus current wheeze, was present in 901 children (18% of the sample), of whom 225 (5%) had moderate asthma, defined as asthma plus additional symptoms (sleep disturbance), utilization (hospital, casualty), or disability (reduced activity, school absence). Use of inhaled corticosteroid/cromoglycate was reported by 636 children (13% of the sample). Determinants of use included: asthma diagnosis, current wheeze, and troublesome dry nocturnal cough. There was also a strong relationship between anti-inflammatory treatment and a multicomponent asthma severity score constructed for each child. Inhaled corticosteroids and/or cromoglycate were used by 56% of the children with asthma (24% daily) and by 76% of children with moderate asthma (42% daily). Undertreatment, defined as less than daily inhaled corticosteroids/cromoglycate in moderate asthma, was identified in 130 children (14% of those with asthma or 3% of the sample). Conversely, apparently aggressive treatment, defined as inhaled corticosteroid/cromoglycate use in children with persistent minimal symptoms (asthma severity score of less than 3) was identified in 101 children (2% of the sample). Although there were significant differences between regions in the choice of anti-inflammatory drugs and in the prevalence both of undertreatment and apparently aggressive treatment, there was no clear relationship to regional utilization of emergency and hospital services for asthma. Nevertheless, the frequency of undertreatment suggests an opportunity to reduce asthma morbidity by more consistent application of current therapeutic guidelines. 相似文献
44.
IA Bukaeva NT Ra?khlin NA Probatova EA Smirnova NN Tupitsyn EN Sholokhova R Gossrau 《Canadian Metallurgical Quarterly》1997,59(4):31-38
26 cases of lymphoproliferative diseases were studied: 8 cases of reactive follicular hyperplasia (RFH), 11 cases of non-Hodgkin's malignant lymphomas (NML), 7 cases of lymphogranulomatosis (LGM). Only gamma-glutamyl transpeptidase (GGT) was found in lymphoid cells of B- and T-dependent areas of lymph nodes with reactive changes as well as in tumor cells of NML and LGM. GGT activity was more pronounced in NML of high-grade malignancy (centroblast and immunoblast) as compared to lymphomas of lower grade of malignancy (lymphocytic, centroblast-centrocytic and in Lennert lymphoma). GGT activity in cells of Hodgkin and Berezovsky-Sterberg in some cases of LGM was high, in others low. Significant differences in GGT activity between RFH and follicular centroblast-centrocytic lymphoma were not found. Activity of aminopeptidase M was observed in histiocytes, fibroblasts, vessels and areas of connective tissue growth. Aminopeptidase A activity was observed in vessels only. Activity of dipeptidyl(amino)peptidase IV was observed in some lymphoid cells in RFH, NML and LGM. Thus, GGT activity may be considered as a differential-diagnostic marker in separating NML of high and low degree of malignancy and this may presume a different sensitivity to the therapy. 相似文献
45.
YM Graus JJ Verschuuren NA Bos PJ van Breda Vriesman MH De Baets 《Canadian Metallurgical Quarterly》1993,43(1-2):113-124
The immunoglobulin heavy chain (VH) gene family usage in experimental autoimmune myasthenia gravis (EAMG) model was investigated by RNA slot blot hybridization using VH gene family specific probes. Anti-acetylcholine receptor (AChR) monoclonal antibodies (mAbs) isolated from susceptible C57BL/6 and resistant BALB/c mice were found to be encoded by VH genes from at least six different families. The Vgam3.8 family was overrepresented in alpha-bungarotoxin blocking mAbs. Expression of cross-reactive idiotypes by anti-AChR mAbs was irrespective of the VH gene family usage. Strain dependent differences in susceptibility for EAMG were not reflected in an aberrant VH gene family usage of anti-AChR mAbs. 相似文献
46.
Twenty-one adult dry-bone sacral specimens were used to quantitatively determine the location of the sacral pedicle, foramina, and ala on the lateral radiographic view of the sacrum. The anterior and posterior sacral foramina from S1 to S3, the midlines of the anterior sacrum and cephalad border of the S1 vertebral body, and the lateral limit of the lateral sacral mass were outlined with wires. A lateral radiograph was taken, and measurements were made directly from the radiograph. The average sacral pedicle height for both male and female specimens was approximately 20 mm for S1, 12 mm for S2, and 7 mm for S3. The sacral foramina height averaged approximately 13 mm for S1 and S2, and 10 mm for S3. The average ala and S1 body-ala angles were 88 degrees and 35 degrees. The distance from the ala tip to the anterior aspect of the sacrum averaged 12 mm, and the average anterior height of the S1 vertebral body above the ala was 11 mm. These measurements, in conjunction with inlet and outlet radiographs, may aid in the recognition of the vital structures of the sacrum on the lateral radiographic view and enhance the safety of dorsal sacral screw placement. 相似文献
47.
R Steinmetz NA Mitchner A Grant DL Allen RM Bigsby N Ben-Jonathan 《Canadian Metallurgical Quarterly》1998,139(6):2741-2747
The xenoestrogen bisphenol A (BPA) has been shown to mimic estrogen both in vivo and in vitro. BPA stimulates PRL secretion and the expression of a PRL regulating factor from the posterior pituitary in the estrogen-sensitive Fischer 344 rat (F344), but not in Sprague-Dawley (SD) rats. The goal of the present studies was to examine the in vivo actions of BPA on the reproductive tract. The specific objectives were 1) to characterize the short term effects of BPA on cell proliferation and c-fos expression in the uterus and vagina, and 2) to compare the effects of prolonged exposure to low doses of BPA on the reproductive tract of F344 and SD rats. Treatment with single high doses of BPA induced cell proliferation in the uterus and vagina of ovariectomized F344 rats, as determined by bromodeoxyuridine immunostaining. This proliferation was dose dependent (from 37.5-150 mg/kg) and followed a time course similar to that of estradiol (E2). Quantitative RT-PCR revealed that both BPA and E2 increased c-fos messenger RNA levels in the uterus 14- to 16-fold within 2 h, which returned to basal levels after 6 h. In the vagina, BPA-induced c-fos expression remained elevated for up to 6 h, compared with the transient increase caused by E2. Treatment of F344 rats for 3 days with continuous release capsules that supplied a much lower dose of BPA (approximately 0.3 mg/kg x day) resulted in hypertrophy, hyperplasia, and mucus secretion in the uterus and hyperplasia and cornification of the vaginal epithelium. The reproductive tract of SD rats did not respond to this treatment paradigm with BPA. These studies demonstrate that 1) the molecular and morphological alterations induced by BPA in the uterus and vagina are nearly identical to those induced by estradiol; 2) the vagina appears to be especially sensitive to the estrogenic actions of BPA; 3) the reproductive tract of the inbred F344 rat appears more sensitive to BPA than that of the outbred SD rat; and 4) continuous exposure to microgram levels of BPA is sufficient for exerting estrogenic actions. 相似文献
48.
K Norose JI Clark NA Syed A Basu E Heber-Katz EH Sage CC Howe 《Canadian Metallurgical Quarterly》1998,39(13):2674-2680
PURPOSE: To determine the role of SPARC (secreted protein, acidic, and rich in cysteine) in cataractogenesis by examining mice deficient in a matricellular protein SPARC. METHODS: Mice were rendered SPARC-deficient by a targeted disruption of the gene. Slit-lamp microscopy and histology were used to examine the eyes of SPARC-null and wild-type mice from birth to 14 months of age. RESULTS: SPARC-null mice developed opacities in the posterior cortex of the eye as early as 1.5 months after birth. The diffuse cataracts appeared to progress toward the anterior cortex and reached maturity in many animals by 3.5 months of age. Early stages of cataractogenesis in SPARC-null mice included inhibition of normal lens fiber cell differentiation, degeneration of fiber cells, vacuole formation at the equator, and liquefaction of the cortex. No cataracts were detected in wild-type mice up to the age of 8 months. CONCLUSIONS: The early onset of cataracts in SPARC-null mice establishes that the gene is essential to the maintenance of lens transparency. 相似文献
49.
50.
Influence of the prenatal hypoinsulinaemia (streptozocin diabetes) on the behaviour of the offsprings of Wistar rats was studied from 1 to 20 postnatal days. In experimental pups there were slower weight increment, later eye opening, later development of elementary behavioural acts (grooming elements, rearing, sniffing), and later formation of complex behavioural patterns (investigation of an environment) than in the control offsprings of healthy females. 相似文献