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1.
Pancreatic islets of the Syrian golden hamster were maintained in culture for extended periods of time. Toxicity of streptozotocin in these cultures was evaluated by measurement of insulin secretion. Exposure of islets to 1 or 2 mM streptozotocin immediately following isolation resulted in a permanent and dose-related inhibition of insulin secretion. This was accompanied by islet disruption as observed by phase-contrast microscopy. Culture of islets for 24 hours before streptozotocin exposure afforded protection from toxicity. For example, exposure of freshly isolated islets to 2 mM streptozotocin resulted in complete destruction of beta cells, whereas islets similarly exposed after a 24 hr culture period continued to secrete insulin for many months. Islets maintained in culture for one week before exposure to 0.1–0.5 mM streptozotocin, however, became more sensitive than freshly isolated islets. Repeated weekly exposure of cultured islets to a non-toxic concentration (0.1 mM) resulted in sustained suppression of insulin secretion after 11 weeks. 相似文献
2.
Mark Tony Lieberman Robert M. Zablotowicz Naida P. Davis-Omholt 《Applied microbiology》1986,51(4):715-719
An improved method for antibiotic resistance recovery of Bradyrhizobium japonicum from soybean (Glycine max (L.) Merr.) nodules that is simple, time saving, and economical was developed. This technique involves the use of two 96-well microtiter plates as a multinodule sterilization chamber and a template and a third plate as a 16-point replicator constructed with steel nails affixed to the plate with epoxy cement. With this system a team of four technicians could type 3,000 nodules per day. This method was useful in assessing strain establishment and interstrain competition when one or more uniquely labeled strains of B. japonicum were inoculated onto either growth-room- or field-grown soybeans. Contamination was low and reproducibility across replicates approached the theoretical upper limit. Simplicity in design and use made this recovery method especially adaptable for field studies in which large numbers of nodules were required to provide a representative statistical sample offering good precision. 相似文献
3.
Media made hyperosmotic with sucrose increase the frequency of spontaneously released quanta of transmitter, or miniature excitatory postsynaptic potentials (MEPSPs). In calcium-free medium, depolarization with high potassium reduces the MEPSP frequency, presumably due to calcium efflux in the reversed gradient condition. This effect of depolarization is blocked by cobalt, supporting the above interpretation of the effects of hypertonicity and depolarization and suggesting that cobalt can block efflux as well as influx through calcium channels. 相似文献
4.
The role of 24,25(OH)2D3 in calcium homeostasis is still controversial. In the present study the administration of low doses of 1,25(OH)2D3 and of higher doses of 24,25(OH)2D3 either alone or in conjunction with each other, were studied in rachitic chicks and in Japanese quails. Whereas 24,25(OH)2D3 alone had no significant effect on duodenal CaBP and on alkaline phosphatase in chick serum, it increased the influence of 1,25(OH)2D3 on these two parameters strongly. Also, when 1,25(OH)2D3 and 24,25(OH)2D3 were given simultaneously to Japanese quails, calcium excretion via the egg shell was clearly higher than when either metabolite had been administered alone. These results indicate that 1,25(OH)2D3 and 24,25(OH)2D3 exert a strong synergistic effect in rachitic animals. 相似文献
5.
4 protein sources were tested for palatability, digestibility, influence on bodyweight and consistency of faeces in Callithrix jacchus and Saguinus fuscicollis. The protein sources were incorporated at crude protein levels of 12, 17 and 22% in a pelleted diet. A banana supplement was also fed which reduced the total protein content to 10.7, 14.7 and 18.3%. The test diets, fed for 3 weeks, were well accepted with the milk proteins being slightly preferred. Consumption of the 12% protein pellets was greater than their 22% equivalents. True protein digestibility was calculated to be 97% for lactalbumin, 96% for casein, 90% for soy protein concentrate and 83% for soyabean meal. Changes in bodyweight were negligible. Dry matter of faeces varied between 25% (lactalbumin diets) and 28% (casein diets), but did not change with increasing protein intake. Increasing levels of cellulose, from 2.4 to 7.2% total crude fibre lowered the apparent protein digestibility from 84.3 to 79.2% and the digestibility of dry matter from 82.2 to 76.5%. 相似文献
6.
The nematode, Caenorhabditis elegans, contains a family of six genes that code for vitellogenins. Here we report the complete nucleotide sequence of one of these genes, vit-5. The gene specifies a mRNA of 4869 nucleotides, including untranslated regions of 9 bases at the 5' end and 51 bases at the 3' end. Vit-5 contains four short introns totalling 218 bp. The predicted vitellogenin, yp170A, has a molecular weight of 186,430. At its N terminus it is clearly related to the vitellogenins of vertebrates. However, the vit-5-encoded protein does not contain a serine-rich sequence related to the vertebrate vitellin, phosvitin. In fact, the amino acid composition of the nematode protein is very similar to that of the vertebrate protein without phosvitin. Vit-5 has a highly asymmetric codon choice dictionary. The favored codons are different from those favored in other organisms, but are characteristic of highly expressed C. elegans genes. The strong selection against rare codons is not as great near the 5' end of the gene; rare codons are 15 times more frequent within the first 54 bp than in the next 4.8 kb. 相似文献
7.
Adult pallids bats collected in April or May, were maintained in short or long photoperiods (10 or 14 h light/day) for 3-6 months. In August, the short-day bats had regressed testes, epididymal spermatozoa and fully developed accessory sex glands, corresponding to the autumnal reproductive condition of field animals; long-day bats had testes undergoing spermatogenesis, few epididymal spermatozoa and undeveloped accessory sex glands (summer reproductive condition). Bats in each photoperiod manifested the expected autumnal reproductive pattern in October. We suggest that photoperiod influences the reproductive physiology of male pallid bats by affecting an endogenous circannual reproductive rhythm. 相似文献
8.
Plasma luteinizing hormone (LH) levels were determined at monthly intervals in intact and ovariectomized squirrels maintained in a constant 14L:10D photoperiod at a temperature of 23 +/- 2 degrees C. LH was undetectable (less than 0.9 ng/ml) in plasma of intact females at all times of year. Females ovariectomized (OVX) at 9.5 months of age in March showed substantial increases in plasma LH in May and June but LH was undetectable between July and November. Females ovariectomized at 13 months of age in July first manifested detectable LH levels the following January and February (6-7 months post-ovariectomy). Very few adult females trapped in May and ovariectomized in August had detectable LH levels within 2 months of ovariectomy; however, females ovariectomized the following February had detectable LH titers 1 month later. Long-term studies of individual OVX squirrels indicated peak LH levels between March and June, 1980, relatively low or undetectable titers between August and December and elevated LH levels between January and March, 1981. The results are suggestive of a circannual rhythm of LH secretion which appears restricted to one season of the year and occurs independently of steroid feedback from the ovaries; ovarian steroids only modulate the levels of plasma LH during the brief annual period of hypothalamo-hypophysial activity. We suggest that onset and termination of LH release are mediated by central nervous system circannual clocks. 相似文献
9.
Improved Solid Medium for the Detection and Enumeration of Pectolytic Bacteria 总被引:7,自引:1,他引:6
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An improved solid agar medium (MP medium) has been developed which allows detection of pectolytic activity in bacteria. Organisms tested exhibited a variety of regulatory controls governing pectate lyase synthesis. The medium contains mineral salts, pectin, and yeast extract. After growth of the organisms, the agar plate is flooded with a polysaccharide precipitant, and pectolytic activity is shown by clear zones around active colonies. High concentrations of phosphate are shown to be necessary for pectic enzyme formation on solid media. The medium has successfully been used to detect pectolytic organisms in soil, forest litter, and rotting vegetable samples. 相似文献
10.
Induction of phenylalanine ammonia-lyase in xanthium leaf discs: increased inactivation in darkness 总被引:3,自引:3,他引:0
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Zucker M 《Plant physiology》1971,47(3):442-444