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101.
The hierarchical structure of metabolic networks and the construction of efficient metabolic simulators 总被引:2,自引:0,他引:2
D J Park 《Journal of theoretical biology》1974,46(1):31-74
Methods are presented for the efficient simulation of large scale metabolic networks based upon the hierarchical structure of such networks and the formation of steady-state aggregations. The methods are dynamic and result in a varying time scale which is always consonant with the response of the network. An algorithm for the generation of reduced equivalent networks is presented. Problems of accuracy and stability are discussed. Special methods such as cascading and telescoping are presented for speeding the solution of the steady-state aggregations. 相似文献
102.
103.
Lipid patterns of embryonal carcinoma cell lines and their derivatives: Changes with differentiation
The lipid composition of several teratocarcinoma cell lines has been examined by biochemical and immunological methods in order to identify properties that might be correlated with the state of cell differentiation. The data indicate qualitative and quantitative changes in the phospholipid, cholesterol, and glycolipid composition. In particular, the ratios of cholesterol/phospholipid and of sphingomyelin/phosphatidylcholine are higher in differentiated cells. Gangliosides with short glycosidic chains (GM3 and GD3) are characteristic of undifferentiated, multipotent, embryonal carcinoma cell lines. More complex gangliosides (GM1 and GD1a) appear early during the course of differentiation. Each differentiated cell line presents a unique ganglioside map. Results are tentatively correlated with a stabilization of the membrane bilayer in differentiated cell lines, whereas a more fluid state of the membrane in embryonal carcinoma cell lines would allow maximal flexibility. Subtle differences in ganglioside composition among embryonal carcinoma cell lines are discussed in relation with their potentialities, and their developmental age. 相似文献
104.
The preservation of Mullerian inhibiting substance during long-term freezing of testicular fragments 总被引:1,自引:0,他引:1
Mullerian Inhibiting Substance, a fetal testicular hormone found in most mammalian species, causes regression in the male of the Mullerian duct, the anlagen of the fallopian tube, uterus, and upper vagina. Limitations to study of this substance in the past have been posed by its short period of production and by its localized and specific action. We have been able to store testicular fragments that continue to demonstrate detectable Mullerian Inhibiting Substance activity for up to 5 months by using techniques of slow freezing which approximate 1 °C/min, cryoprotective additives, storage in liquid nitrogen, and rapid thawing. These fragments then can be pooled for biochemical and endocrinological studies. In addition, unknown fragments can be transported long distances for assay of Mullerian Inhibiting Substance. 相似文献
105.
In 1858, Edward Hitchcock named Sphaerapus larvalis and S. magnus for burrows from the nonmarine Lower Jurassic Turners Falls Formation in Massachusetts. Walpia hermitensis White, 1929, from the Lower Permian Hermit Shale, Arizona, is also a little known ichnotaxon. Examination of the type material indicates that Sphaerapus is a senior subjective synonym of Walpia. Sphaerapus is also a nomen oblitum, but Walpia has not been sufficiently used to replace its senior synonym as a conserved name; thus, we use the senior synonym Sphaerapus as the valid name of this ichnogenus, which is monospecific (S. larvalis = S. magnus = W. hermitensis). Numerous specimens of Sphaerapus from the Lower Permian of New Mexico and Texas, and a new record from the Lower Jurassic of Massachusetts show that it is a horizontal endichnion or exichnion having an unpacked tunnel with a cylindrical to ellipsoidal cross section, in some specimens branching, and lined with flattened, lenticular, non-coprolitic sediment pellets that are irregularly arranged and in some specimens imbricated. The pellets distinguish Sphaerapus from other endichnia. Sphaerapus resembles burrows of recent variegated mud-loving beetles and mole crickets, so Sphaerapus was likely produced by a hexapod similarly adapted for subsurface, compaction burrowing. Variation in pellet shape and arrangement in Sphaerapus reflects fluidity of the sediment burrowed, so this variation is a taphonomic artifact of no ichnotaxonomic significance. The latest Wolfcampian first appearance of Sphaerapus is not facies related, as similar facies lacking Sphaerapus are present in middle-late Wolfcampian strata. Therefore, the first appearance of Sphaerapus may reflect the evolutionary first appearance of a hexapod that moved through the sediment by compaction tunneling. However, the stratigraphically disjunct distribution of Sphaerapus may indicate that its preservation and fossilization were sensitive to paleoenvironmental and/or taphonomic factors that may also be involved in its first appearance. 相似文献
106.
The frequency of long-calling in untreated and hormone-treated juvenile laughing gulls was compared. While both estrogen and testosterone increased the calling rate, testosterone was more effective for both sexes. Both estrogen- and testosterone-treated males called more often than similarly treated females. As both sexes normally call in laughing gulls, these results were compared to the more usual situation where only males of the species sing. Possible control mechanisms were discussed. 相似文献
107.
108.
Guillermo Castorena Stuart Lind Fabrizio Michelassi Peter Huttemeier W. David Watkins Warren M. Zapol 《Prostaglandins & other lipid mediators》1984,28(5):695-709
Zymosan activated plasma infusion induces pulmonary sequestration of neutrophils and the release of TXA2 into the pulmonary vascular bed causing profound and transient pulmonary hypertension.Since ethanol (ETOH) inhibits several inflammatory functions of neutrophils, including adherence and aggregation, we examined the ability of anesthetic doses of ETOH to alter the hemodynamic and cellular response to the infusion of zymosan activated plasma (ZAP) in vivo. Twenty five ml of autologous ZAP was intravenously infused into five control and seven (ETOH-treated sheep during mechanical ventillation. In control sheep the mean pulmonary artery pressure (PAP) transiently increased from 14.7±1.4 mm Hg (mean±SEM) to a pead of 38+8 mm Hg by three minutes after beginning the infusion of ZAP. Blood leukocyte concentration transiently decreased 19% below the baseline value due to pulmonary sequestration of polymorphonuclear leukocytes (PMN). Plasma TXB2 levels measured by radioimmunoassay (RIA) increased from 0.2 to 5.4 ng/ml six minutes after the initiation of ZAP infusion.In five sheep, intravenous infusion of 200 ml of 96% ETOH yielded very high plasma concentrations (882±101 mg%) and completely inhibited both the rise of PAP and the increase of plasma TXB2 levels after ZAP infusion. However, blood leukocytes transiently decreased 58% below the baseline value. Lower plasma levels of ETOH (200 and 400 mg%) did not prevent either the increase of PAP or the elevation of plasma TXB2 after ZAP infusion. 相似文献
109.
Collisions with wind turbines are an increasing conservation concern for migratory birds that already face many threats. Existing collision‐risk models take into account parameters of wind turbines and bird flight behavior to estimate collision probability and mortality rates. Two behavioral characteristics these models require are the proportion of birds flying at the height of the rotor swept‐zone and the flight speed of birds passing through the rotor swept‐zone. In recent studies, investigators have measured flight height and flight speed of migrating birds using fixed‐beam radar and thermal imaging. These techniques work well for fixed areas where migrants commonly pass over, but they cannot readily provide species‐specific information. We measured flight heights of a nesting shorebird, the federally threatened Piping Plover (Charadrius melodus), using optical range finding and measured flight speed using videography. Several single‐turbine wind projects have been proposed for the Atlantic coast of the United States where they may pose a potential threat to these plovers. We studied Piping Plovers in New Jersey and Massachusetts during the breeding seasons of 2012 and 2013. Measured flight heights ranged from 0.7 to 10.5 m with a mean of 2.6 m (N = 19). Concurrent visually estimated flight heights were all within 2 m of measured heights and most within 1 m. In separate surveys, average visually estimated flight height was 2.6 m (N = 1674) and ranged from 0.25 m to 40 m. Average calculated flight speed was 9.30 m/s (N = 17). Optical range finding was challenging, but provided a useful way to calibrate visual estimates where frames of reference were lacking in the environment. Our techniques provide comparatively inexpensive, replicable procedures for estimating turbine collision‐risk parameters where the focus is on discrete nesting areas of specific species where birds follow predictable flight paths. 相似文献
110.
JAY L. CLAUSEN MARILYN HOYT ELIZABETH WESSLING BRYCE STEARNS BOSCO RAMIREZ NIC KORTE 《Soil & Sediment Contamination》2004,13(3):245-254
The use of sodium bisulfate for field preservation of soil samples collected for the analysis of volatile organics (VOCs) can result in the formation of acetone. The work was performed at Camp Edwards, Massachusetts, as part of a multi-year investigation of the effects of training activities on the local environment. Preservation with sodium bisulfate was initiated in 1999 under regulatory mandate. The frequency of acetone detection and the quantities reported increased immediately thereafter. Correlation of duplicate sample results and a side-by-side comparison of six sample handling methods involving two analytical laboratories suggest the interaction of sodium bisulfate with naturally occurring organic matter in samples from Camp Edwards cause the formation of acetone. The data also indicate that a higher content of natural organic matter results in a greater production of acetone, and more acetone is formed the longer the sodium bisulfate is in contact with the soil. 相似文献