全文获取类型
收费全文 | 4880篇 |
免费 | 70篇 |
国内免费 | 72篇 |
专业分类
电工技术 | 28篇 |
综合类 | 52篇 |
化学工业 | 89篇 |
金属工艺 | 22篇 |
机械仪表 | 43篇 |
建筑科学 | 51篇 |
矿业工程 | 13篇 |
能源动力 | 6篇 |
轻工业 | 113篇 |
水利工程 | 15篇 |
石油天然气 | 49篇 |
武器工业 | 6篇 |
无线电 | 84篇 |
一般工业技术 | 62篇 |
冶金工业 | 4262篇 |
原子能技术 | 1篇 |
自动化技术 | 126篇 |
出版年
2024年 | 4篇 |
2023年 | 7篇 |
2022年 | 10篇 |
2021年 | 24篇 |
2020年 | 15篇 |
2019年 | 12篇 |
2018年 | 25篇 |
2017年 | 21篇 |
2016年 | 18篇 |
2015年 | 26篇 |
2014年 | 29篇 |
2013年 | 40篇 |
2012年 | 48篇 |
2011年 | 54篇 |
2010年 | 50篇 |
2009年 | 51篇 |
2008年 | 48篇 |
2007年 | 41篇 |
2006年 | 49篇 |
2005年 | 47篇 |
2004年 | 25篇 |
2003年 | 29篇 |
2002年 | 14篇 |
2001年 | 15篇 |
2000年 | 14篇 |
1999年 | 142篇 |
1998年 | 1389篇 |
1997年 | 734篇 |
1996年 | 469篇 |
1995年 | 263篇 |
1994年 | 223篇 |
1993年 | 260篇 |
1992年 | 40篇 |
1991年 | 52篇 |
1990年 | 64篇 |
1989年 | 53篇 |
1988年 | 59篇 |
1987年 | 61篇 |
1986年 | 49篇 |
1985年 | 60篇 |
1983年 | 5篇 |
1982年 | 18篇 |
1981年 | 26篇 |
1980年 | 26篇 |
1979年 | 5篇 |
1978年 | 7篇 |
1977年 | 84篇 |
1976年 | 199篇 |
1975年 | 6篇 |
1955年 | 3篇 |
排序方式: 共有5022条查询结果,搜索用时 15 毫秒
991.
992.
BH Cohen RJ Packer KR Siegel LB Rorke G D'Angio LN Sutton DA Bruce L Schut 《Canadian Metallurgical Quarterly》1993,19(4):171-179
Survival for children with brain tumors less than 2 years of age at diagnosis is dismal, and the quality of life of long-term survivors poor. Between 1975 and 1987, 78 (13%) of 579 patients with brain tumors treated at Children's Hospital of Philadelphia were under 2 years of age. Tumor site was posterior fossa in 31 (40%) and supratentorial in 47 (60%). Nine of 37 patients (24%) with malignant tumors, and 30 of 41 (73%) patients with benign tumors are alive with a mean follow-up of 116 months. Long-term survival after treatment with chemotherapy alone occurred in 10 patients, including 3 with malignant tumors. In 5 additional patients, chemotherapy delayed the need for irradiation a mean of 30 months. Of the 29 patients who relapsed after initial therapy, 12 are alive without progressive disease (2 patients with malignant tumors and 10 with benign tumors) a mean of 80 months after relapse, 2 children are alive with progressive disease, and 14 died a median of 48 months (range 9-115 months) after relapse. Twenty-one of the 39 survivors have minimal or no neurological or intellectual dysfunction. Surviving patients treated with surgery and chemotherapy have better intellectual function than patients treated with surgery and radiation (with or without chemotherapy) in that 8 of 10 children treated with surgery and chemotherapy have normal or above normal intelligence compared with 5 of 12 children receiving irradiation before their second birthday. 相似文献
993.
EE Sanidas MI Filipe J Linehan NR Lemoine WJ Gullick T Rajkumar DA Levison 《Canadian Metallurgical Quarterly》1993,54(6):935-940
The pattern of c-erbB-3 gene product was studied in 91 advanced gastric carcinomas, adjacent hyperplastic mucosa, intestinal metaplasia and dysplasia and in normal controls, using immunohistochemistry in archival material. All tumours showed positive c-erbB-3 staining in both cytoplasm and membrane. No significant differences of expression were observed between intestinal and diffuse-type carcinomas or any other clinical parameters. Of interest is the expression in the adjacent mucosa, which is extensive, cytoplasmic, and of lower intensity than in the tumours. Further studies are currently being carried out to clarify the role of this protein in tumour behaviour and gastric carcinogenesis. 相似文献
994.
995.
ML Israel DA Connolly RE von Heyn JM Rock PW Smith 《Canadian Metallurgical Quarterly》1993,24(4):343-355
Fifty-two case-hardened, severely self-abusive and aggressive autistic and retarded students, living in six different community residences, were trained to exit their residences, without the presence or assistance of staff, when a fire alarm sounded at night. On a pretest, prior to an 11-week period of intensive environmental and behavioral interventions, only 25% of the students exited within 2 1/2 minutes and independent of staff assistance. At posttest, 100% exited successfully, in a mean evacuation time of 60 seconds. The study was conducted at the Behavior Research Institute (BRI). 相似文献
996.
SC Langley GW Rickett A Hunt FJ Kelly AD Postle DA York 《Canadian Metallurgical Quarterly》1993,45(3):543-551
The biochemical maturation of the lung in late gestation and in the young animal is regulated by glucocorticoids. The present study was aimed at dissociating the different glucocorticoid receptor sites involved in these regulatory functions. The obese Zucker rat was selected as a model for this study as it exhibits hypersensitivity to glucocorticoid hormone action by virtue of its elevated receptor numbers and activity. Two synthetic steroid analogues were administered to obese animals; RU28362, a specific type II receptor agonist, and the type II antagonist RU486. RU28362 promoted a strong catabolic effect, which was associated with reduced food intake and the abolition of growth in the rats. The agonist, RU28362, attenuated developmental increases in antioxidant enzyme activities, and altered the growth of the tissue. At the age studied, development of the lung phosphatidylcholine (PC) system was almost complete, but RU28362 increased disaturated PC 16:0/16:0 concentrations by almost 2-fold, and altered the molecular composition of total pulmonary PC. RU486 attenuated the growth of the rats and reduced their food intake. Treatment with the type II antagonist attenuated lung growth and increased the activities of pulmonary copper zinc (Cu/Zn) and manganese (Mn) superoxide dismutases. RU486 had no effect on lung PC concentrations and molecular composition. The data suggest a role for type I glucocorticoid receptors in the regulation of the antioxidant enzyme system in the lung, as type II antagonism will channel endogenous glucocorticoid binding to the type I site. Type II receptor binding would appear to play a role in regulating the lung PC content. 相似文献
997.
998.
JK Barnett D Barnett CA Bolin TA Summers EA Wagar NF Cheville RA Hartskeerl DA Haake 《Canadian Metallurgical Quarterly》1999,67(2):853-861
The outer membrane of pathogenic Leptospira species grown in culture media contains lipopolysaccharide (LPS), a porin (OmpL1), and several lipoproteins, including LipL36 and LipL41. The purpose of this study was to characterize the expression and distribution of these outer membrane antigens during renal infection. Hamsters were challenged with host-derived Leptospira kirschneri to generate sera which contained antibodies to antigens expressed in vivo. Immunoblotting performed with sera from animals challenged with these host-derived organisms demonstrated reactivity with OmpL1, LipL41, and several other proteins but not with LipL36. Although LipL36 is a prominent outer membrane antigen of cultivated L. kirschneri, its expression also could not be detected in infected hamster kidney tissue by immunohistochemistry, indicating that expression of this protein is down-regulated in vivo. In contrast, LPS, OmpL1, and LipL41 were demonstrated on organisms colonizing the lumen of proximal convoluted renal tubules at both 10 and 28 days postinfection. Tubular epithelial cells around the luminal colonies had fine granular cytoplasmic LPS. When the cellular inflammatory response was present in the renal interstitium at 28 days postinfection, LPS and OmpL1 were also detectable within interstitial phagocytes. These data establish that outer membrane components expressed during infection have roles in the induction and persistence of leptospiral interstitial nephritis. 相似文献
999.
Between 1992 and 1996 the number of health maintenance organizations (HMOs) entering the Medicaid market grew at an average annual rate of approximately 22 percent. Participation among all ownership segments grew, resulting in a broad distribution of beneficiaries across the HMO industry. However, recent declines in financial performance within the industry appear to be more dramatic for plans with many Medicaid members. In addition, growing concerns about rate adequacy and volatility as well as expanding administrative demands raise questions about the long-term commitment of commercial HMOs to Medicaid participation. This paper analyzes operating characteristics and financial performance of licensed commercial HMOs from 1992 through 1996, drawing on indepth interviews with health plan executives and managed care stock analysts. 相似文献
1000.
DA Bushinsky MA Bashir DR Riordon Y Nakagawa FL Coe MD Grynpas 《Canadian Metallurgical Quarterly》1999,55(2):602-612
BACKGROUND: Human calcium oxalate (CaOx) nephrolithiasis may occur if urine is supersaturated with respect to the solid-phase CaOx. In these patients, dietary oxalate is often restricted to reduce its absorption and subsequent excretion in an effort to lower supersaturation and to decrease stone formation. However, dietary oxalate also binds intestinal calcium which lowers calcium absorption and excretion. The effect of increasing dietary oxalate on urinary CaOx supersaturation is difficult to predict. METHODS: To determine the effect of dietary oxalate intake on urinary supersaturation with respect to CaOx and brushite (CaHPO4), we fed 36th and 37th generation genetic hypercalciuric rats a normal Ca diet (1.2% Ca) alone or with sodium oxalate added at 0.5%, 1.0%, or 2.0% for a total of 18 weeks. We measured urinary ion excretion and calculated supersaturation with respect to the CaOx and CaHPO4 solid phases and determined the type of stones formed. RESULTS: Increasing dietary oxalate from 0% to 2.0% significantly increased urinary oxalate and decreased urinary calcium excretion, the latter presumably due to increased dietary oxalate-binding intestinal calcium. Increasing dietary oxalate from 0% to 2.0% decreased CaOx supersaturation due to the decrease in urinary calcium offsetting the increase in urinary oxalate and the decreased CaHPO4 supersaturation. Each rat in each group formed stones. Scanning electron microscopy revealed discrete stones and not nephrocalcinosis. X-ray and electron diffraction and x-ray microanalysis revealed that the stones were composed of calcium and phosphate; there were no CaOx stones. CONCLUSION: Thus, increasing dietary oxalate led to a decrease in CaOx and CaHPO4 supersaturation and did not alter the universal stone formation found in these rats, nor the type of stones formed. These results suggest the necessity for human studies aimed at determining the role, if any, of limiting oxalate intake to prevent recurrence of CaOx nephrolithiasis. 相似文献