全文获取类型
收费全文 | 3020篇 |
免费 | 40篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 3篇 |
综合类 | 1篇 |
化学工业 | 200篇 |
金属工艺 | 33篇 |
机械仪表 | 19篇 |
建筑科学 | 50篇 |
矿业工程 | 1篇 |
能源动力 | 27篇 |
轻工业 | 157篇 |
水利工程 | 35篇 |
石油天然气 | 7篇 |
无线电 | 68篇 |
一般工业技术 | 87篇 |
冶金工业 | 2274篇 |
原子能技术 | 4篇 |
自动化技术 | 95篇 |
出版年
2023年 | 5篇 |
2022年 | 10篇 |
2021年 | 36篇 |
2020年 | 16篇 |
2019年 | 16篇 |
2018年 | 21篇 |
2017年 | 21篇 |
2016年 | 29篇 |
2015年 | 22篇 |
2014年 | 36篇 |
2013年 | 65篇 |
2012年 | 53篇 |
2011年 | 63篇 |
2010年 | 50篇 |
2009年 | 46篇 |
2008年 | 43篇 |
2007年 | 39篇 |
2006年 | 41篇 |
2005年 | 24篇 |
2004年 | 24篇 |
2003年 | 29篇 |
2002年 | 31篇 |
2001年 | 18篇 |
2000年 | 13篇 |
1999年 | 68篇 |
1998年 | 641篇 |
1997年 | 388篇 |
1996年 | 225篇 |
1995年 | 122篇 |
1994年 | 118篇 |
1993年 | 146篇 |
1992年 | 23篇 |
1991年 | 27篇 |
1990年 | 20篇 |
1989年 | 35篇 |
1988年 | 31篇 |
1987年 | 36篇 |
1986年 | 27篇 |
1985年 | 25篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 17篇 |
1981年 | 17篇 |
1980年 | 28篇 |
1978年 | 4篇 |
1977年 | 90篇 |
1976年 | 190篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1955年 | 5篇 |
排序方式: 共有3061条查询结果,搜索用时 0 毫秒
21.
The use of photodynamic dye and light inactivation for the treatment of genital herpes simplex virus infections has been associated with the risk of potential oncogenesis. Sixteen patients treated with neutral red and fluorescent light for documented herpetic infections were studied at intervals ranging from 9 to 52 months following treatment. Four patients treated with other modalities were included in the study. Biopsies of the treated areas were obtained, and 3925 tissue sections were examined. Mild atypical epithelial changes were focally present in most specimens regardless of therapy. Histologically identifiable premalignant change could not be demonstrated. 相似文献
22.
To demonstrate the presence of independent genetic determinants of multiple correlated tooth dimensions from twin data, a multivariate analysis was performed on the covariance matrices of monozygotic and dizygotic within-pair differences for mesiodistal and buccolingual dimensions of 28 teeth of the secondary dentition. The results provided strong evidences that the correlation among tooth dimensions is primarily genetic in origin, probably attributable to the pleiotropic action of either independent genes or groups of genes. Among the genetic factors that were identified, one appeared to affect the maxillary teeth in general while a second influenced primarily the anterior mandibular teeth. There was a striking tendency for homologous measurements on the right and left sides to be associated with the same genetic factor. In contrast, genetic determination of the maxillary and mandibular dentition seemed to be independent of each other, and a wider range of genetic factors were found to influence the mandibular than the maxillary teeth, suggesting that a differential degree of evolutionary stability may have been achieved in the teeth of the two jaws. 相似文献
23.
24.
Although iodine prevents goiter, enlarged thyroid glands continue to be detected in subjects, especially children, in spite of adequate iodine ingestion. Iodine may cause goiter in susceptible individuals by inhibiting the organic binding of iodine as is seen in adult asthmatics, neonates born of iodine ingesting mothers and in subjects residing along the littoral of Japan. Myxedema, especially in treated Graves' disease and Hashimoto's disease, may also be precipitated by iodine. On the other hand, iodine given to euthyroid subjects in areas of endemic goiter and to subjects with nontoxic nodular goiter may induce thyrotoxicosis by disclosing diffuse autonomously functioning thyroid tissue. An indirect adverse effect of iodine upon the thyroid gland may be manifested by lymphocyte glandular infiltrates and chronic thyroiditis which were sparse or absent in thyroid glands removed from subjects living in iodine deficient areas before iodine prophylaxis and therapy. Not only has the incidence of thyroiditis increased, but the histologic and clinical distinctions between treated Graves' disease and chronic thyroiditis have become indistinct. Experimentally, chronic thyroiditis has been produced in animals following large doses of iodine. Accumulated evidence supports the concept that iodine contributes to the genesis of chronic thyroiditis. 相似文献
25.
Activation of the alternative complement pathway by respiratory secretory IgA was demonstrated by incubating purified, aggregated preparations of serum and secretory IgA with neat human serum. No depletion of the early components (C1-4) was observed, but 63 and 70% of C3-9, respectively, were consumed. The C3-9-consuming capacity of heat-aggregated nasal secretions from an IgA-deficient volunteer was compared with heat-aggregated nasal secretions from a normal volunteer known to have secretory IgA. The deficient secretions consumed C3-9, whereas the IgA deficient secretions did not. Reconstitution of the nasal secretions from the IgA-deficient volunteer with purified secretory IgA produced alternative pathway activation. Factor B of the alternative complement pathway was found to be present in 16 of 18 bronchoalveolar lavage samples (BALF) from normal volunteers. Simultaneous measurement of lavage and serum albumin and Factor B concentrations rendered it unlikely that Factor B was merely a transudative product from serum in half the samples but rather suggested that it may be a component of lower respiratory tract secretions. The presence of an intact alternative complement pathway in BALF was indicated by showing that cobra venom factor and endotoxin cleaved functionally pure human C3 when mixed with BALF, but had no effect on C3 in the absence of BALF. 相似文献
26.
We have followed the growth of stature, sitting height, skinfolds, muscle widths measured radiologically, and skeletal maturity in growth hormone-deficient patients in whom hGH was given and withheld in alternating three-month periods throughout puberty (referred to as "off-hGH" and "on-hGH" periods). Six boys and four girls had true isolated GH deficiency and developed puberty spontaneously. Two boys had gonadotrophin deficiency plus GH deficiency, and five boys had multiple deficiencies; in these boys the signs of puberty were induced by hormone treatment. Boys with true isolated deficiency grew about two-thirds as much in height in the off-hGH periods as in the on-hGH periods; their total gain in height during the adolescent spurt would have been about 20 cm, instead of 30 cm, if hGH had been discontinued at the beginning of puberty. The effect of hGH was entirely on growth in leg-length, however, which virtually ceased during the off-hGH periods. Growth in sitting height altered little when hGH was withdrawn. Growth in limb muscles, however, was GH dependent throughout puberty; during the majority of periods when hGH was withheld, muscle was actually lost; this occurred in the boys who were receiving large doses of testosterone as well as in those producing their own normal amounts. Subcutaneous fat diminished when hGH was given and increased when it was withdrawn; this occurred independently of administration of testosterone. There was little evidence that growth of pubic and axillary hair progressed faster during on-hGH periods, except perhaps in patients with multiple deficiencies. There was some evidence, however, that bone age progressed less rapidly during on-hGH periods than during off-hGH periods in the patients with isolated deficiency. The results in the girls agreed with those in boys so far as stature was concerned, but the relationship with sitting height and leg length appeared to be different; the reasons for this are discussed. We conclude that all children with GH deficiency should continue on treatment with hGH throughout puberty, ideally until growth ceases. 相似文献
27.
Oocytes from CBA mice varying in age from 2 to 11 months were cultured to the metaphase II stage of meiosis and the chromosomes analyzed. The oocytes from three maternal age groups were compared with respect to the mean number of oocytes obtained per mouse, the frequency of maturation to metaphase II, and the frequency of numerical chromosomes abnormalities. Both the mean number of oocytes obtained per mouse and the frequency of maturation decreased markedly with maternal age. The frequency of chromosome abnormalities in the oocytes increased with maternal age from the young to the middle-aged mice but dropped off in the oldest maternal age group. No hyperploid (n + 1) oocytes were observed in the young or old group of mice, but 5.2% hyperploidy occurred in the middle-aged group. It is suggested that the lack of hyperploid oocytes in the old CBA females might be due to a threshold effect in which oocytes that are damaged by the number of univalents present at metaphase I become atretic and do not progress to metaphase II. The frequency of diploid (2n) oocytes was 1.7% and was not maternal-age dependent. 相似文献
28.
K Solez RJ D'Agostini RA Buono N Vernon AL Wang PM Finer RH Heptinstall 《Canadian Metallurgical Quarterly》1976,85(3):555-568
A significant number of offspring from brother-sister matings of NIH-Okamoto-Aoki spontaneously hypertensive rats (SHRs) were found to be normotensive at 20 weeks of age. Over 20% of the animals that were hypertensive at this age had mild-to-moderate unilateral hydronephrosis at the time of sacrifice. In over 90% of the rats that did not develop hypertension spontaneously, ligation of one ureter raised blood pressure above 150 mm Hg within 2 weeks. In those rats made hypertensive by obstructing one ureter and in those that developed hypertension with accompanying naturally occurring hydronephrosis, subcutaneous implants of fragmented renal medulla from unrelated normal rats decreased blood pressure to normotensive levels. In contrast, medullary implants had no significant effect in rats developing hypertension spontaneously without hydronephrosis. Renal inner medullary plasma flow was low in the obstructed kidneys of hydronephrotic hypertensive SHRs but was elevated in the kidneys of nonhydronephrotic hypertensive SHRs. The hypertension in hydronephrotic SHRs appears to be related to an impairment of the antihypertensive function of the renal medulla. Such an impairment of medullary antihypertensive function does not appear to play a significant role in the hypertension in SHRs without hydronephrosis. 相似文献
29.
Comparison of human and hamster mitochondrial transfer RNA. Physical properties and methylation status 总被引:1,自引:0,他引:1
In a comparative study, the effective of intraventricularly or intraperitoneally injected p-chloroamphetamine (p-CA) and some chloroindoles on cerebral levels of serotonin was evaluated. 5-Chloroindole depressed 5-HT levels in the brainstem and telencephalon for three days, 6-chloro-2-methylindole (6-CMI) only during the first day. 5-Chloroindazole had no effect at all. p-CA was more toxic to guinea pigs than to rats. p-CA and 5-chloro-2-methylindole (5-CMI) had no effect on cerebral 5-HT in chicks. Apparently, none of these compounds represented or was converted to a metabolite possibly responsible for the neurotoxic effects of p-CA. 相似文献
30.
A comparison of the effects of left stellate ganglion stimulation (SGS) on central and aortic hemodynamics has been made in chloralose-anesthetized mongrel (M), and greyhound (GH) dogs. Measurements of aortic pressure and flow, and left ventricular pressure were made during stimulation of the decentralized left SG at different frequencies from 0 to 20 Hz. The increases in aortic pressure and flow with SGS were larger in the GH, especially for low frequencies of stimulation. Stroke volume was increased with SGS in the GH at all stimulation rates, whereas in the M it was unchanged. A greater decrease in left ventricular end-diastolic pressure with SGS was found in the GH. These results suggest that differences exist in both the intrinsic and extrinsic control of cardiac output in the greyhound dog compared to the mongrel. These differences may be in part responsible for the elevated arterial blood pressure in the greyhound compared to the mongrel. 相似文献