全文获取类型
收费全文 | 1981篇 |
免费 | 195篇 |
国内免费 | 1篇 |
出版年
2021年 | 19篇 |
2020年 | 15篇 |
2018年 | 19篇 |
2017年 | 15篇 |
2016年 | 32篇 |
2015年 | 61篇 |
2014年 | 57篇 |
2013年 | 71篇 |
2012年 | 106篇 |
2011年 | 86篇 |
2010年 | 54篇 |
2009年 | 64篇 |
2008年 | 83篇 |
2007年 | 75篇 |
2006年 | 86篇 |
2005年 | 78篇 |
2004年 | 58篇 |
2003年 | 60篇 |
2002年 | 89篇 |
2001年 | 72篇 |
2000年 | 79篇 |
1999年 | 53篇 |
1998年 | 30篇 |
1997年 | 24篇 |
1996年 | 23篇 |
1995年 | 16篇 |
1994年 | 23篇 |
1993年 | 18篇 |
1992年 | 51篇 |
1991年 | 48篇 |
1990年 | 40篇 |
1989年 | 38篇 |
1988年 | 41篇 |
1987年 | 30篇 |
1986年 | 29篇 |
1985年 | 37篇 |
1984年 | 25篇 |
1983年 | 21篇 |
1982年 | 19篇 |
1981年 | 17篇 |
1979年 | 27篇 |
1978年 | 11篇 |
1977年 | 21篇 |
1976年 | 19篇 |
1974年 | 14篇 |
1973年 | 11篇 |
1972年 | 18篇 |
1971年 | 17篇 |
1969年 | 21篇 |
1967年 | 11篇 |
排序方式: 共有2177条查询结果,搜索用时 15 毫秒
11.
12.
We have isolated the delta-globin gene of the New-World spider monkey,
Ateles geoffroyi, and compared its nucleotide sequence with those of other
primate delta- and beta-globin genes. Among primate delta-globin genes, the
rate of nonsynonymous substitutions is much less than the rate of
synonymous substitutions. This suggests that primate delta- globin genes
may remain under evolutionary conservation, perhaps because hemoglobin A2
has an as yet unknown physiological importance.
相似文献
13.
A E Hardman P R Jones N G Norgan A Hudson 《European journal of applied physiology and occupational physiology》1992,65(4):354-359
The purpose of this study was to examine the influence of brisk walking on endurance fitness and the amount and distribution of body fat in previously sedentary women. Twenty eight women [mean age (SEM): 44.9 (1.5) years] followed the walking programme for 1 year, whilst 16 acted as controls [age 44.4 (2.3) years]. Changes in endurance fitness were evaluated by measuring the oxygen uptake (VO2) at a reference blood lactate concentration of 2 mmol.l-1. Two 1.61-km field tests of walking were completed, one at maximal speed and one at a "brisk" speed, as well as a 1.61-km walk on a motorised treadmill. The amount and distribution of body fat was determined by hydrostatic weighing and anthropometry and energy intake was evaluated using the 7-day weighed food intake method. Walkers completed an average of 157 min.week-1 of brisk walking over the year. The following were increased in walkers, relative to controls: brisk walking speed [walkers 1.73 (0.05) m.s-1 vs 1.88 (0.07) m.s-1; controls 1.69 (0.05) m.s-1 vs 1.70 (0.05) m.s-1 at baseline and 12 months respectively, P < 0.01], maximal walking speed and VO2 at 2 mmol.l-1. In addition, brisk walking reduced heart rate and blood lactate concentration during stepping as well as during standard, submaximal treadmill walking. It did not modify either the amount or the distribution of body fat, despite an unchanged energy intake. 相似文献
14.
D A Hudson 《Comparative biochemistry and physiology. B, Comparative biochemistry》1992,102(4):701-706
1. Secretion of pulse-labelled protein by the isolated epithelium of guinea-pig seminal vesicle epithelium was rapid, unaffected by cholinergic and adrenergic drugs, cyclic nucleotides or changes in the sodium, potassium and calcium concentrations of the "chase" medium. 2. Low temperature, NH4Cl, hyper- and hypo-osmolarity and membrane-stabilizing agents inhibited secretion which was also dependent on aerobic metabolism. 3. Monensin reduced secretion of the six labelled, relatively low molecular weight proteins recovered from the medium in a concentration-dependent, apparently non-specific manner. 相似文献
15.
LCR/MEL: a versatile system for high-level expression of heterologous proteins in erythroid cells. 总被引:11,自引:0,他引:11 下载免费PDF全文
M Needham C Gooding K Hudson M Antoniou F Grosveld M Hollis 《Nucleic acids research》1992,20(5):997-1003
We have used the human globin locus control region (LCR) to assemble an expression system capable of high-level, integration position-independent expression of heterologous genes and cDNAs in murine erythroleukaemia (MEL) cells. The cDNAs are inserted between the human beta-globin promoter and the second intron of the human beta-globin gene, and this expression cassette is then placed downstream of the LCR and transfected into MEL cells. The cDNAs are expressed at levels similar to those of the murine beta-globin in the induced MEL cells. Heterologous genomic sequences can also be expressed at similar levels when linked to to the LCR and beta-globin promoter. In addition we demonstrate that, after induction of differentiation, MEL cells are capable of secreting heterologous proteins over a prolonged time period, making this system suitable for use in continuous production systems such as hollow fibre bioreactors. The utility of the LCR/MEL cell system is demonstrated by the expression of growth hormone at high levels (greater than 100 mg/l) 7 days after induction. Since the expression levels seen do not depend upon gene amplification and are independent of the integration position of the expression cassette, it is possible to obtain clones with stable high-level expression within 3-4 weeks after transfection. 相似文献
16.
R W Yost S J Grauvickel R Cantwell J S Bomalaski A P Hudson 《Biochemistry international》1991,24(2):199-208
We demonstrate that both phospholipase A1 and phospholipase A2 are associated with isolated yeast mitochondria (Saccharomyces cerevisiae). Activity assays indicate that, unlike most other mitochondrial phospholipases A, the yeast enzymes are Ca(2+)-independent with acidic (pH 4-5) as well as alkaline (pH 8-9) pH optima. Data obtained with mitochondria isolated from either fermenting or respiring cells, and initial observations with a petite strain, strongly suggest that a phospholipase A2 with an acidic pH optimum functions in the in vivo adaptation and maintenance of mitochondrial membranes required for respiration. 相似文献
17.
A. J. Swerdlow A. J. Douglas G. V. Hudson B. V. Hudson M. H. Bennett K. A. MacLennan 《BMJ (Clinical research ed.)》1992,304(6835):1137-1143
OBJECTIVE--To analyse the risk of second primary cancers during long term follow up of patients with Hodgkin''s disease. DESIGN--Cohort study. SETTING--The British National Lymphoma Investigation (a collaborative group of over 60 participating centres in Britain treating lymphomas). PATIENTS--2846 patients first treated for Hodgkin''s disease during 1970-87, for whom follow up was complete in 99.8%. MAIN OUTCOME MEASURES--Second primary cancers; uniform pathology reviews confirmed the diagnosis of Hodgkin''s disease and of second primary non-Hodgkin''s lymphomas. RESULTS--113 second primary cancers occurred. Relative risk of cancer other than Hodgkin''s disease was 2.7 (95% confidence interval 2.3 to 3.3) compared with the general population, with significant risk of leukaemia (16.0(9.1 to 26.0)); non-Hodgkin''s lymphoma (16.8(9.8 to 26.9)); and cancers of the colon (3.2 (1.4 to 6.2)), lung (3.8 (2.6 to 5.4)), bone (15.1 (1.8 to 54.7)), and thyroid (9.4 (1.1 to 33.9)). Absolute excess risk associated with treatment was greater for solid tumours than for leukaemia and lymphomas. Relative risk of leukaemia increased soon after treatment, reaching a peak after five to nine years. It was increased substantially after chemotherapy (27.9 (12.7 to 52.9)), combined treatment with radiotherapy and chemotherapy (21.5 (7.9 to 46.8)), and relative to number of courses of chemotherapy but was not significantly increased after radiotherapy (2.5 (0.1 to 14.1)). Relative risk of non-Hodgkin''s lymphoma increased in the first five years after treatment and remained high but showed no clear relation with type or extent of treatment. Relative risk of solid tumours was less raised initially but increased throughout follow up and for lung cancer 10 years or more after entry was 8.3 (4.0 to 15.3). The risk of solid tumours increased after treatments including radiotherapy and after chemotherapy alone. The risk after chemotherapy increased significantly with time since first treatment. CONCLUSION--The risk of solid cancer, not of leukaemia, is the major long term hazard of treatment for Hodgkin''s disease, and this seemed to apply after chemotherapy as well as after radiotherapy. These risks of second cancers are important in choice of treatment and in follow up of patients, but they are small compared with the great improvements in survival which have been brought about by modern therapeutic methods for Hodgkin''s disease. 相似文献
18.
OBJECTIVE--To assess the implementation of action protocols dictated by antenatal risk factors noted at the initial (booking) antenatal visit. DESIGN--Retrospective study of 2000 women delivered between 1 March 1990 and 29 March 1991. SETTING--Maternity department of a district general hospital supporting a multiethnic population in inner London. MAIN OUTCOME MEASURES--Comparison of clinical actions performed against those dictated by the department''s protocols. Analysis according to clinical importance, gestation at booking, maternal age, parity, birth order, ethnic origin, and certainty of gestational age. RESULTS--Interobserver agreement between the two auditors was good (kappa statistic for risk factors detected, 0.78; for actions generated, 0.80). Of the 15,658 actions dictated by department protocols, 3673 (23.5%) were actually performed by the clinicians. The 63 combinations of risk factors and actions believed by consultants to be of particular clinical importance had an action rate of 28.3% compared with 18.6% for those considered less important (p < 0.001). Mothers who first visited the hospital antenatal clinic at or before 24 weeks'' gestation had 25.2% of relevant protocols fulfilled (p < 0.001). Compliance was significantly improved in women aged 36 or over (32.4%), black women (24.9%), and cases of uncertain gestation (24.5%). Parity and birth order were not associated with an altered action rate. Ethnic origin deemed as "other" (than white, black, Asian, or oriental) or "unknown" was associated with poor compliance (19.3%). CONCLUSIONS--Compliance to a set of agreed protocols was poor even though a computer system was available and a protocol manual had been distributed. Protocols were more likely to be implemented in women who booked early and in some groups of women deemed at high risk including older mothers, black women, and those denoted as having uncertain gestational age. 相似文献
19.
20.
Specific cDNA and oligonucleotide probes were used to study the appearance of transthyretin mRNA in developing rat brain using Northern gel analysis, cytoplasmic dot hybridization, and in situ hybridization. Transthyretin mRNA in embryonic rat brain was found to be confined to the epithelial layer of the choroid plexus primordia appearing first in the fourth ventricle, followed by appearance in the lateral ventricles, and subsequently in the third ventricle. Transthyretin mRNA was localized in these cells from early stages of neuroepithelium differentiation, showing that it is a sensitive marker for the differentiation of the choroid plexus within the fetal brain. 相似文献