全文获取类型
收费全文 | 2287篇 |
免费 | 35篇 |
国内免费 | 8篇 |
专业分类
电工技术 | 11篇 |
综合类 | 16篇 |
化学工业 | 24篇 |
金属工艺 | 16篇 |
机械仪表 | 7篇 |
建筑科学 | 14篇 |
矿业工程 | 6篇 |
能源动力 | 1篇 |
轻工业 | 17篇 |
水利工程 | 9篇 |
石油天然气 | 4篇 |
无线电 | 26篇 |
一般工业技术 | 60篇 |
冶金工业 | 2066篇 |
原子能技术 | 1篇 |
自动化技术 | 52篇 |
出版年
2024年 | 3篇 |
2023年 | 4篇 |
2022年 | 3篇 |
2021年 | 7篇 |
2020年 | 7篇 |
2019年 | 5篇 |
2018年 | 6篇 |
2017年 | 2篇 |
2016年 | 2篇 |
2015年 | 7篇 |
2014年 | 7篇 |
2013年 | 13篇 |
2012年 | 14篇 |
2011年 | 22篇 |
2010年 | 13篇 |
2009年 | 20篇 |
2008年 | 15篇 |
2007年 | 14篇 |
2006年 | 6篇 |
2005年 | 12篇 |
2004年 | 4篇 |
2003年 | 12篇 |
2002年 | 9篇 |
2001年 | 4篇 |
2000年 | 5篇 |
1999年 | 76篇 |
1998年 | 634篇 |
1997年 | 367篇 |
1996年 | 234篇 |
1995年 | 135篇 |
1994年 | 127篇 |
1993年 | 144篇 |
1992年 | 16篇 |
1991年 | 20篇 |
1990年 | 11篇 |
1989年 | 16篇 |
1988年 | 28篇 |
1987年 | 23篇 |
1986年 | 16篇 |
1985年 | 18篇 |
1983年 | 2篇 |
1982年 | 12篇 |
1981年 | 14篇 |
1980年 | 22篇 |
1978年 | 7篇 |
1977年 | 63篇 |
1976年 | 113篇 |
1975年 | 7篇 |
1966年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有2330条查询结果,搜索用时 15 毫秒
91.
A Shaner LJ Roberts TA Eckman JM Racenstein DE Tucker JW Tsuang J Mintz 《Canadian Metallurgical Quarterly》1998,49(5):684-690
OBJECTIVE: This study determined the sources and frequency of diagnostic uncertainty for patients with chronic psychosis and active cocaine abuse or dependence and assessed the usefulness of prospective follow-up in clarifying diagnosis. METHODS: A total of 165 male patients with chronic psychoses and cocaine abuse or dependence on inpatient units of a Veterans Affairs medical center were evaluated using the Structured Clinical Interview for DSM-III-R (SCID-R), urine tests, hospital records, and interviews with collateral sources. An algorithm allowing key SCID-R items and diagnostic criteria to be designated as provisionally met or uncertain was applied, resulting in a provisional diagnosis and a list of alternate diagnoses. The assessment was repeated 18 months later in an attempt to resolve diagnostic uncertainty. RESULTS: In 30 cases (18 percent), initial assessment produced a definitive diagnosis, including 21 cases of schizophrenia, six of schizoaffective disorder, and three of psychostimulant-induced psychotic disorder. In the other 135 cases, a definitive diagnosis could not be reached because of one or more sources of diagnostic uncertainty, including insufficient periods of abstinence (78 percent), poor memory (24 percent), and inconsistent reporting (20 percent). Reassessment at 18 months led to definitive diagnoses in 12 additional cases. CONCLUSIONS: It was frequently difficult to distinguish schizophrenia from chronic substance-induced psychoses. Rather than concluding prematurely that psychotic symptoms are, or are not, substance induced, clinicians should initiate treatment of both psychosis and the substance use disorder in uncertain cases. The persistence or resolution of psychosis during abstinence and additional history from the stabilized patient or collateral sources may clarify the diagnosis. 相似文献
92.
PM Sutaria M Ohebshalom TA McCaffrey ED Vaughan D Felsen 《Canadian Metallurgical Quarterly》1998,62(21):1965-1972
Transforming growth factor-beta (TGF-beta) is a profibrotic cytokine which has been implicated in the renal fibrosis which follows unilateral ureteral obstruction (UUO) in the rat. TGF-beta receptor type I (TGF-RI) and TGF-beta receptor type II (TGF-RII) are part of the complex which mediates the response to TGF-beta. We sought to determine if TGF-RI and TGF-RII are found in the kidney, and if their expression is changed as a result of UUO. Polymerase chain reaction (PCR) was used to determine expression of mRNA for TGF-RI and TGF-RII in the kidney. Immunoperoxidase was used to localize and quantify the expression of these receptors at 3, 7, 14, 21 and 28 days after UUO, and in sham-operated animals. Expression of mRNA for TGF-RI and TGF-RII was demonstrated in sham operated, obstructed and contralateral unobstructed kidneys using PCR. Using immunoperoxidase, a uniform distribution of TGF-RI and TGF-RII was found in cortical tubules of sham operated kidneys, whereas medullary tubules showed a patchy TGF-RI distribution and no TGF-RII staining. After UUO, an increased tubular expression of TGF-RI and TGF-RII was noted in both obstructed and contralateral kidneys compared to sham operated kidneys. No staining for either TGF-RI or TGF-RII was noted in glomeruli, vasculature or interstitial cells. TGF-beta receptors I and II were found exclusively in renal tubules and were shown to increase in both the obstructed and contralateral kidneys relative to sham operated animals. Upregulation of TGF-beta receptors in both kidneys suggests that TGF-beta may contribute to the fibrotic response in the obstructed kidney and the hypertrophic response of the contralateral kidney. 相似文献
93.
This study analyzes the changes in costs and prices from 1986 to 1994 for more than 3,500 U.S. short-term general hospitals, including 122 horizontal mergers. These mergers were generally financially beneficial to consumers, providing average price reductions of approximately 7 percent. Merger-related price reductions were considerably less in market areas with higher market concentration levels. Merger-related price reductions in areas with higher penetration by health maintenance organizations (HMOs) were approximately twice those in areas with lower HMO penetration. Merger-related price reductions were greater for low-occupancy hospitals, nonteaching hospitals, nonsystem hospitals, similar-size hospitals, and hospitals with greater premerger service duplication. 相似文献
94.
95.
96.
TA Kuether GM Nesbit WM Clark SL Barnwell 《Canadian Metallurgical Quarterly》1997,41(2):427-32; discussion 432-3
OBJECTIVE: Symptomatic dynamic changes in blood flow secondary to vertebral artery compression with rotational head motion are evaluated in a series of patients as a cause for posterior circulation transient ischemic attacks. These cases are classic examples of rotational vertebral artery occlusion and allow for the discussion of the anatomic basis, angiographic features, and treatment options. ILLUSTRATIVE CASES: In our series, symptoms of vertebrobasilar insufficiency were reproducible with rotational head movement. Compression of the vertebral artery was demonstrated angiographically. The correct site of occlusion of the vertebral artery was apparent only by dynamic angiography with progressive head rotation. All of the patients presented in the illustrative cases had occlusion at the C2 level; however, one patient had been previously misdiagnosed and another had an additional site of occlusion. The anatomic course of the vertebral artery is described in addition to the sites of rotational occlusion. CONCLUSION: Rotational vertebral occlusion is an important cause of vertebrobasilar symptoms, which may lead to permanent neurological deficit if left undiagnosed. Dynamic angiography is the established method of diagnosis. Great care must be taken to avoid misdiagnosing the site of occlusion or missing a second occlusive site. For this reason, it is crucial to have a thorough understanding of the anatomic course of the vertebral artery and the muscular and tendinous insertions, which may cause rotational occlusion. The decision for treatment must be based on the site of occlusion as well as the assessment of the patient as a surgical candidate. A review of the literature reveals that surgical treatment is effective and must be considered to avoid further morbidity. 相似文献
97.
Within public health discourse there is growing recognition that the social structures and ecology of neighbourhoods impact on health and wellbeing. A clearer understanding of the pathways through which this influence occurs will inform locality-based interventions to tackle inequalities. In this paper we report on an interview based study with parents of young children living in Massey, a suburban neighbourhood of metropolitan Auckland. Locational access to community resources is comparatively poor in Massey as measured by a community resource accessibility index. The findings provide insights into the impact of such access to services and amenities on neighbourhood social cohesion. We conclude by suggesting planning strategies for strengthening neighbourhood identification and attachment for this population group. 相似文献
98.
Tenascin is a large extracellular matrix molecule expressed at specific sites in the adult, including immune system tissues such as the bone marrow, thymus, spleen, and T cell areas of lymph nodes. Tenascin has been reported to have both adhesive and anti-adhesive effects in static assays. We report here that tenascin supports the tethering and rolling of lymphocytes and lymphoblastic cell lines under flow conditions. Binding was calcium dependent and was not inhibited by treatment of lymphocytes with O-glycoprotease or a panel of glycosidases including neuraminidase and heparitinase but was inhibited by treatment of cells with proteinase K. Binding was to the fibrinogen-like terminal domain of tenascin as determined by antibody blocking studies and binding to recombinant tenascin proteins. When compared to rolling of the same cell type on E-selectin, rolling on tenascin was found to be smoother at all shear stresses tested, suggesting that cells formed a larger number of bonds on the tenascin substrate than on the E-selectin substrate. When protein plating densities were adjusted to give similar profiles of cell detachment under increasing shears, the density of tenascin was 8.5-fold greater than that of E-selectin. Binding to tenascin was not dependent on any molecules previously identified as tenascin receptors and is likely to involve a novel tenascin receptor on lymphocytes. We postulate that the ability of tenascin to support lymphocyte rolling may reflect its ability to support cell migration and that this interaction may be used by lymphocytes migrating through secondary lymphoid organs. 相似文献
99.
The experiment was carried out in a combinedblowing converter.The natural gas was supplied asthe cooling medium for the bottom lance.The blow-ing practice of medium P hot metal(0.30-0.85% [P]) indicated that with better stirringat the bottom of the converter and lower P_(CO),thissteelmgking process was favorable to reduce theamount of [C] and [O] and increase the (P_2O_5)/[P].The maximum rate of dephospborization might behigh up to 0.0a5%/min and the P content in steelcould be reduced to lower than 0.03% by singleslag-forming operation. 相似文献
100.