全文获取类型
收费全文 | 1279篇 |
免费 | 11篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 12篇 |
化学工业 | 83篇 |
金属工艺 | 10篇 |
机械仪表 | 25篇 |
建筑科学 | 33篇 |
能源动力 | 14篇 |
轻工业 | 50篇 |
水利工程 | 2篇 |
石油天然气 | 3篇 |
无线电 | 60篇 |
一般工业技术 | 184篇 |
冶金工业 | 684篇 |
原子能技术 | 12篇 |
自动化技术 | 121篇 |
出版年
2022年 | 4篇 |
2021年 | 5篇 |
2019年 | 5篇 |
2018年 | 9篇 |
2017年 | 5篇 |
2016年 | 4篇 |
2015年 | 11篇 |
2014年 | 7篇 |
2013年 | 46篇 |
2012年 | 23篇 |
2011年 | 23篇 |
2010年 | 25篇 |
2009年 | 26篇 |
2008年 | 29篇 |
2007年 | 32篇 |
2006年 | 29篇 |
2005年 | 27篇 |
2004年 | 18篇 |
2003年 | 26篇 |
2002年 | 14篇 |
2001年 | 21篇 |
2000年 | 14篇 |
1999年 | 29篇 |
1998年 | 201篇 |
1997年 | 109篇 |
1996年 | 75篇 |
1995年 | 56篇 |
1994年 | 53篇 |
1993年 | 51篇 |
1992年 | 17篇 |
1991年 | 12篇 |
1990年 | 18篇 |
1989年 | 18篇 |
1988年 | 14篇 |
1987年 | 20篇 |
1986年 | 15篇 |
1985年 | 15篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1981年 | 16篇 |
1980年 | 12篇 |
1979年 | 9篇 |
1978年 | 10篇 |
1977年 | 28篇 |
1976年 | 48篇 |
1975年 | 9篇 |
1974年 | 7篇 |
1973年 | 6篇 |
1972年 | 4篇 |
排序方式: 共有1293条查询结果,搜索用时 15 毫秒
1.
Two Caribbean hair sheep breeds, the St. Croix (SC) and Barbados Blackbelly (BB), are found in the United States, and the SC has led to the development of the Katahdin (K), a synthetic breed of hair sheep. These breeds have mature ewe BW ranging from 32 to 54 kg (for BB and SC) and from 55 to 73 kg (K). Hair sheep and hair sheep crosses have lower rectal temperatures and respiration rates than wool breeds and a lower DMI and water intake. There are indications of increased resistance to internal parasites in hair sheep. Although hair sheep are seasonal breeders under U.S. photoperiodic conditions, they tend to perform better under accelerated lambing systems than traditional wool breeds. Fertility, prolificacy, and lamb survival is high in BB and SC, but hair x wool crossbred ewes tend to have a higher level of fertility than hair and wool parent breeds. Ewe productivity is also higher in hair x wool crosses than in wool crosses, particularly when adjusted for ewe BW or under accelerated lambing systems. Hair sheep have a lower ADG and intake of high-energy diets, as well as a lower gain/feed ratio, than wool breeds. Growth rates tend to be higher in SC than in BB. Differences in carcass characteristics are inconsistent between hair and wool breeds. Production characteristics of hair sheep, particularly hair x wool crosses, make them suitable for low-input, sustainable production systems that do not require high growth rates and large carcasses. There is a need to preserve the existing U.S. hair sheep germplasm base in support of such systems. 相似文献
2.
KL Hopkins PK Dickson TI Ball RR Ricketts PA O'Shea CR Abramowsky 《Canadian Metallurgical Quarterly》1997,32(10):1476-1479
Fetus-in-fetu is an unusual condition in which a vertebrate fetus is enclosed within the abdomen of another fetus. These occurrences are usually benign. This report describes an instance of malignant recurrence after resection of a fetus-in-fetu. 相似文献
3.
Dan C. DeBorde William W. Woessner Bruce Lauerman Patrick Ball 《Water research》1998,32(12):3781-3785
At the present time, somatic and male-specific coliphage and human enterovirus groups are being considered as indicators of possible pathogenic human enteric virus contamination from fecal contamination. A primary attribute for any indicator of fecal contamination is its prevalence at the source and in associated ground water. It must be consistently found in the source material at concentrations that are measurable with available techniques. Over a period of ten months, male-specific and somatic coliphage ranged from 7000 to 4,000,000 PFU/L in the effluent from a multi-user septic-tank. Unlike the values determined for septic-tank effluent, coliphage concentrations measured in ground water over this same period only varied by five-fold. Coliphage concentration in ground water under the down-gradient edge of the drainfield contained 1000 PFU/L. This concentration decreased at −1 log10/5 m during 17.4 m of ground-water transport. From these data, coliphage concentrations in septic-tank effluent seem sufficient to allow their use as indicators of fecal contamination in ground water. 相似文献
4.
K Stelwagen DG Grieve JS Walton JL Ball BW McBride 《Canadian Metallurgical Quarterly》1993,76(4):992-1001
Twenty-five primigravid ewes were used to investigate the effect of bST, between 97 and 124 d of gestation, on mammogenesis and subsequent milk production. Five ewes (reference group) were slaughtered at 96 d of gestation, and the remaining ewes were injected daily with saline (control group: n = 10) or .1 mg/kg of BW of bST (bST group: n = 10). Following bST treatment, 5 control and 5 bST group ewes were slaughtered (slaughter group). The remaining ewes were slaughtered after lambing and being milked for 8 wk (production group). Weekly blood samples were obtained from both slaughter and production group ewes. Slaughter group ewes were also subjected to 8-h serial blood sampling at 98 d (period 1) and 123 d (period 2) of gestation. Milk production was 42% higher in ewes treated prepartum with bST than in those treated with saline. Results suggest that the increase in milk was due to an increase in mammary parenchymal cell number rather than to an increase in cellular activity. The high rate of [3H]thymidine incorporation into parenchymal tissue in reference group ewes suggests that the increase in parenchyma during the second trimester of gestation is due to cellular hyperplasia but that cellular hypertrophy may be more important during the last trimester. Plasma IGF-I concentrations were significantly higher during bST treatment and remained elevated between daily injections; the increase was greatest in period 2. 相似文献
5.
We report two patients with ileal carcinoid tumours which were associated with polyps due to mucosal granulation tissue proliferation. In both cases the tumours had extensively infiltrated the small bowel wall and mesentery, and one had hepatic metastases. The mucosal surface of each specimen showed numerous, pale brown, sessile polyps which were restricted to the intestinal segment involved by carcinoid tumour, although not always closely related to neoplastic cells. The polyps were formed by the proliferation of capillaries, smooth muscle cells and myofibroblasts as demonstrated by immunohistochemistry and electronmicroscopy. 相似文献
6.
7.
8.
9.
JM Cummings RO Parra JA Boullier 《Canadian Metallurgical Quarterly》1995,45(3):414-8; discussion 418-20
OBJECTIVES: An evolving technology for the treatment of bladder outlet obstruction due to benign prostatic hyperplasia (BPH) is the use of the side-firing neodymium: yttrium-aluminum-garnet (Nd:YAG) laser to achieve prostatic tissue ablation. The purpose of this study was to determine the short-term efficacy of this procedure in both an objective and subjective manner. METHODS: We examined this technique by carefully evaluating our first 25 men undergoing the procedure. Each patient was subjected to careful symptom score analysis using the American Urological Association symptom index and multichannel urodynamics, including pressure-flow studies both preoperatively and at 3 months postoperatively. RESULTS: At the 3-month follow-up, symptom scores improved from a preoperative mean of 11.4 to 7.2 and the mean maximum flow rate improved from 6.1 to 14.5 cc/s. These are both significant at P < 0.001. Statistically similar improvement was seen in detrusor pressure at opening and at maximum flow. Eighty percent of the men studied had at least a 50% reduction in symptom score and a 50% improvement in flow rate. CONCLUSIONS: We conclude that laser prostatectomy is a promising minimally invasive treatment for bladder outlet obstruction secondary to BPH and deserves further evaluation at longer terms of follow-up. 相似文献
10.
Eric Keto Roger Ball John Arens Garrett Jernigan Margaret Meixner 《Journal of Infrared, Millimeter and Terahertz Waves》1992,13(11):1709-1725
We present a characterization of some processes affecting the performance of solid state array cameras designed for ground based astronomical imaging in the 8–13μm atmospheric window. Our discussion includes a novel model for electron-hole generationrecombination noise based on the probable pathlength of an electron in a photoconductor. We use the Berkeley mid-IR Array Camera as an example. For this camera, the results show that the total optical system composed of the camera, a 3m telescope, and the atmosphere has an efficiency of about 3%, a 1σ noise equivalent flux density of 25 mJy min?1/2arcsec?2 measured over a Δλ/λ=10% band width, and a noise equivalent expressed as the ambient temperature thermal black body noise of 23%. 相似文献